diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..b641120
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,59 @@
+name: CI Tests
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        operating-system: [ ubuntu-latest ]
+        php: [ '7.4', '8.0' ]
+
+    name: PHP ${{ matrix.php }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          tools: composer:v2
+          coverage: none
+          ini-values: expose_php=1
+
+      - name: Validate composer.json and composer.lock
+        run: composer validate
+
+      - name: Get Composer Cache Directory
+        id: composer-cache
+        run: |
+          echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress
+
+      - name: Run spec tests
+        run: composer tests-spec
+
+      - name: Run tests suite
+        run: composer tests
+
+      - name: Run phpstan
+        run: composer analyze
+
+      - name: Run codestyle checker
+        run: composer cs-check
+
+      - uses: actions/cache@v1
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-composer-
diff --git a/.gitignore b/.gitignore
index 0a60947..9a8c46e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 .idea/
 vendor
 composer.lock
+.phpunit.result.cache
+/data/
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 1727505..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,22 +0,0 @@
-dist: trusty
-language: php
-
-matrix:
-  include:
-    - php: 5.6
-    - php: hhvm
-    - php: 7.0
-    - php: 7.1
-    - php: nightly
-  allow_failures:
-    - php: nightly
-  fast_finish: true
-
-before_install:
-
-install:
-  - composer install
-
-script:
-   - vendor/bin/phpspec run --no-interaction
-   - vendor/bin/phpunit tests
diff --git a/README.md b/README.md
index 4bcb02c..14bee5e 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,8 @@
 PHP Structure Check
 ===================
 
-[![Build Status](https://travis-ci.org/1blankz7/php-structure-check.svg?branch=master)](https://travis-ci.org/1blankz7/php-structure-check)
-[![Latest Stable Version](https://poser.pugx.org/1blankz7/php-structure-check/v/stable)](https://packagist.org/packages/1blankz7/php-structure-check)
-[![Total Downloads](https://poser.pugx.org/1blankz7/php-structure-check/downloads)](https://packagist.org/packages/1blankz7/php-structure-check)
-[![License](https://poser.pugx.org/1blankz7/php-structure-check/license)](https://packagist.org/packages/1blankz7/php-structure-check)
+[![Build Status](https://travis-ci.org/CubiclDev/php-structure-check.svg?branch=master)](https://travis-ci.org/CubiclDev/php-structure-check)
+[![License](https://poser.pugx.org/cubicl/php-structure-check/license)](https://packagist.org/packages/cubicl/php-structure-check)
 
 This library can check a complex array structure against a given requirement.
 The purpose of this library is to create a better experience when testing a result set from an api or something similar.
@@ -12,7 +10,7 @@ The purpose of this library is to create a better experience when testing a resu
 ## Installation
 
 ```
-composer require 1blankz7/php-structure-check
+composer require cubicl/php-structure-check
 ```
 
 ## Usage
@@ -84,6 +82,7 @@ Currently the following types are supported:
  * Datetime
  * Regex
  * Optional
+ * Enum
  
 There are some open issues with ideas for more types. Feel free to send pull requests.
 
diff --git a/composer.json b/composer.json
index 22fe000..edac254 100644
--- a/composer.json
+++ b/composer.json
@@ -1,29 +1,54 @@
 {
-    "name":         "1blankz7/php-structure-check",
-    "description":  "Structural check of arrays for PHP 5.6+",
-    "keywords":     ["array", "structure", "types"],
-    "homepage":     "https://github.com/1blankz7/php-structure-check",
-    "type":         "library",
-    "license":      "MIT",
-    "authors":      [
-        {
-            "name":      "Christian Blank",
-            "email":     "mail@cblank.de",
-            "homepage":  "http://cblank.de"
-        }
+  "name": "cubicl/php-structure-check",
+  "description": "Structural check of arrays for PHP 7.4+",
+  "keywords": [
+    "array",
+    "structure",
+    "types"
+  ],
+  "homepage": "https://github.com/cubicldev/php-structure-check",
+  "type": "library",
+  "license": "MIT",
+  "authors": [
+    {
+      "name": "Christian Blank",
+      "email": "christian@cubicl.de",
+      "homepage": "https://cubicl.de"
+    }
+  ],
+  "scripts": {
+    "check": [
+      "@analyze",
+      "@tests",
+      "@tests-spec",
+      "@cs-check"
     ],
-    "require-dev": {
-        "phpspec/phpspec": "^3.2",
-        "phpunit/phpunit": "^5.6"
-    },
-    "autoload": {
-        "psr-4": {
-            "StructureCheck\\": [
-                "src"
-            ],
-            "StructureCheck\\Test\\": [
-                "tests"
-            ]
-        }
+    "tests": "phpunit tests",
+    "analyze": "phpstan analyse --level max",
+    "tests-spec": "phpspec run --no-interaction",
+    "cs-check": "phpcs --parallel=50",
+    "cs-fix": "phpcbf"
+  },
+  "require-dev": {
+    "phpspec/phpspec": "^6.2",
+    "phpunit/phpunit": "^9.4",
+    "phpstan/phpstan": "^0.12.51",
+    "phpstan/phpstan-deprecation-rules": "^0.12.4",
+    "phpstan/phpstan-phpunit": "^0.12.16",
+    "squizlabs/php_codesniffer": "^3.5.5"
+  },
+  "autoload": {
+    "psr-4": {
+      "Cubicl\\StructureCheck\\": [
+        "src"
+      ],
+      "Cubicl\\StructureCheck\\Test\\": [
+        "tests"
+      ]
     }
+  },
+  "require": {
+    "ext-json": "*",
+    "php": "^7.4|^8.0"
+  }
 }
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
new file mode 100644
index 0000000..1c5e692
--- /dev/null
+++ b/phpcs.xml.dist
@@ -0,0 +1,21 @@
+<?xml version = "1.0"?>
+<ruleset name="PSR12 coding standard">
+    <!-- display progress -->
+    <arg value="p"/>
+    <arg name="colors"/>
+
+    <!-- inherit rules from: -->
+    <rule ref="PSR12">
+        <exclude name="Generic.Files.LineLength"/>
+    </rule>
+    <rule ref="Generic.Arrays.DisallowLongArraySyntax"/>
+    <rule ref="Squiz.WhiteSpace.SuperfluousWhitespace">
+        <properties>
+            <property name="ignoreBlankLines" value="false"/>
+        </properties>
+    </rule>
+
+    <!-- Paths to check -->
+    <file>src</file>
+    <file>tests</file>
+</ruleset>
\ No newline at end of file
diff --git a/phpspec.yml b/phpspec.yml
index 2a4150f..42b140e 100644
--- a/phpspec.yml
+++ b/phpspec.yml
@@ -1,4 +1,4 @@
 suites:
   structure_check_suite:
-    namespace: StructureCheck
-    psr4_prefix: StructureCheck
\ No newline at end of file
+    namespace: Cubicl\StructureCheck
+    psr4_prefix: Cubicl\StructureCheck
\ No newline at end of file
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..da420ab
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,9 @@
+includes:
+  - vendor/phpstan/phpstan-phpunit/extension.neon
+  - vendor/phpstan/phpstan-deprecation-rules/rules.neon
+parameters:
+  tmpDir: data
+  level: max
+  paths:
+    - src
+    - tests
\ No newline at end of file
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
new file mode 100644
index 0000000..a2d1acc
--- /dev/null
+++ b/phpunit.xml.dist
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation = "./vendor/phpunit/phpunit/phpunit.xsd"
+         cacheResultFile="./data/phpunit.result.cache"
+         colors                        = "true">
+    <testsuites>
+        <testsuite name="Unit">
+            <directory suffix="Test.php">./tests/</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>
\ No newline at end of file
diff --git a/spec/Check/CountCheckSpec.php b/spec/Check/CountCheckSpec.php
index e1c08c3..6a53485 100644
--- a/spec/Check/CountCheckSpec.php
+++ b/spec/Check/CountCheckSpec.php
@@ -1,12 +1,14 @@
 <?php
 
-namespace spec\StructureCheck\Check;
+declare(strict_types=1);
 
-use StructureCheck\Check\CountCheck;
+namespace spec\Cubicl\StructureCheck\Check;
+
+use Cubicl\StructureCheck\Check\CountCheck;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
-use StructureCheck\ResultInterface;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class CountCheckSpec extends ObjectBehavior
 {
@@ -27,20 +29,20 @@ function it_implements_type_interface(TypeInterface $child)
     function it_returns_a_result_on_invalid_child_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(false);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 1);
 
-        $this->check([])->shouldHaveType(ResultInterface::class);
+        $this->check('', [])->shouldHaveType(ResultInterface::class);
     }
 
     function it_returns_a_result_on_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(true);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 1);
 
-        $this->check([3])->shouldHaveType(ResultInterface::class);
+        $this->check('', [3])->shouldHaveType(ResultInterface::class);
     }
 }
diff --git a/spec/Check/NumericRangeCheckSpec.php b/spec/Check/NumericRangeCheckSpec.php
index b0fe05c..ae71910 100644
--- a/spec/Check/NumericRangeCheckSpec.php
+++ b/spec/Check/NumericRangeCheckSpec.php
@@ -1,12 +1,14 @@
 <?php
 
-namespace spec\StructureCheck\Check;
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck\Check;
 
 use Prophecy\Argument;
-use StructureCheck\Check\NumericRangeCheck;
+use Cubicl\StructureCheck\Check\NumericRangeCheck;
 use PhpSpec\ObjectBehavior;
-use StructureCheck\ResultInterface;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class NumericRangeCheckSpec extends ObjectBehavior
 {
@@ -28,20 +30,20 @@ function it_implements_type_interface(TypeInterface $child)
     function it_returns_a_result_on_invalid_child_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(false);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 0, 1);
 
-        $this->check(Argument::any())->shouldHaveType(ResultInterface::class);
+        $this->check('', Argument::any())->shouldHaveType(ResultInterface::class);
     }
 
     function it_returns_a_result_on_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(true);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 0, 1);
 
-        $this->check(0)->shouldHaveType(ResultInterface::class);
+        $this->check('', 0)->shouldHaveType(ResultInterface::class);
     }
 }
diff --git a/spec/CheckerSpec.php b/spec/CheckerSpec.php
index b351b52..ad2a345 100644
--- a/spec/CheckerSpec.php
+++ b/spec/CheckerSpec.php
@@ -1,27 +1,30 @@
 <?php
 
-namespace spec\StructureCheck;
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck;
 
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Checker;
-use StructureCheck\ResultInterface;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Checker;
+use Cubicl\StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class CheckerSpec extends ObjectBehavior
 {
-    function it_is_initializable()
+    function it_is_initializable(): void
     {
         $this->shouldHaveType(Checker::class);
     }
 
-    function it_accepts_a_type_and_an_array_as_parameter_for_fulfills(TypeInterface $type)
+    function it_accepts_a_type_and_an_array_as_parameter_for_fulfills(TypeInterface $type, ResultInterface $result)
     {
+        $type->check('', [])->willReturn($result);
         $this->fulfills([], $type);
     }
 
     function it_returns_the_result_of_the_type_in_fulfills(TypeInterface $type, ResultInterface $result)
     {
-        $type->check([])->willReturn($result);
+        $type->check('', [])->willReturn($result);
         $this->fulfills([], $type)->shouldBe($result);
     }
 }
diff --git a/spec/ResultSpec.php b/spec/ResultSpec.php
index b3149e7..2a5c2bb 100644
--- a/spec/ResultSpec.php
+++ b/spec/ResultSpec.php
@@ -1,9 +1,11 @@
 <?php
 
-namespace spec\StructureCheck;
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck;
 
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Result;
+use Cubicl\StructureCheck\Result;
 
 class ResultSpec extends ObjectBehavior
 {
@@ -28,7 +30,7 @@ function it_will_return_is_invalid_if_it_was_set_in_constructor()
 
     function it_will_return_an_empty_array_if_no_error_list_is_given()
     {
-        $this->beConstructedWith(true);
+        $this->beConstructedWith(true, []);
         $this->getErrors()->shouldHaveCount(0);
     }
 }
diff --git a/spec/Type/AnyTypeSpec.php b/spec/Type/AnyTypeSpec.php
index 26b6cf9..43b428f 100644
--- a/spec/Type/AnyTypeSpec.php
+++ b/spec/Type/AnyTypeSpec.php
@@ -1,8 +1,10 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\AnyType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\AnyType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
@@ -15,25 +17,25 @@ function it_is_initializable()
 
     function it_should_return_valid_for_null()
     {
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 
     function it_should_return_empty_errors_for_null()
     {
-        $this->check(null)->getErrors()->shouldHaveCount(0);
+        $this->check('', null)->getErrors()->shouldHaveCount(0);
     }
 
     function it_should_return_valid_for_all_values()
     {
-        $this->check(true)->isValid()->shouldBe(true);
-        $this->check("foo")->isValid()->shouldBe(true);
-        $this->check(13)->isValid()->shouldBe(true);
+        $this->check('', true)->isValid()->shouldBe(true);
+        $this->check('', "foo")->isValid()->shouldBe(true);
+        $this->check('', 13)->isValid()->shouldBe(true);
     }
 
     function it_should_return_empty_errors_for_all_values()
     {
-        $this->check(true)->getErrors()->shouldHaveCount(0);
-        $this->check("foo")->getErrors()->shouldHaveCount(0);
-        $this->check(13)->getErrors()->shouldHaveCount(0);
+        $this->check('', true)->getErrors()->shouldHaveCount(0);
+        $this->check('', "foo")->getErrors()->shouldHaveCount(0);
+        $this->check('', 13)->getErrors()->shouldHaveCount(0);
     }
 }
diff --git a/spec/Type/BoolTypeSpec.php b/spec/Type/BoolTypeSpec.php
index aac647f..aae328c 100644
--- a/spec/Type/BoolTypeSpec.php
+++ b/spec/Type/BoolTypeSpec.php
@@ -1,9 +1,11 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck\Type;
 
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Type\BoolType;
+use Cubicl\StructureCheck\Type\BoolType;
 
 class BoolTypeSpec extends ObjectBehavior
 {
@@ -15,16 +17,16 @@ function it_is_initializable()
 
     function it_should_return_valid_for_bool()
     {
-        $this->check(true)->isValid()->shouldBe(true);
-        $this->check(false)->isValid()->shouldBe(true);
+        $this->check('', true)->isValid()->shouldBe(true);
+        $this->check('', false)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1)->isValid()->shouldBe(false);
-        $this->check(1.0)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1)->isValid()->shouldBe(false);
+        $this->check('', 1.0)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/DatetimeTypeSpec.php b/spec/Type/DatetimeTypeSpec.php
index 27ed724..3008718 100644
--- a/spec/Type/DatetimeTypeSpec.php
+++ b/spec/Type/DatetimeTypeSpec.php
@@ -1,35 +1,37 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\DatetimeType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\DatetimeType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
 class DatetimeTypeSpec extends ObjectBehavior
 {
-    function it_is_initializable()
+    public function it_is_initializable(): void
     {
         $this->beConstructedWith('d-m-Y h:m:s', 'UTC');
         $this->shouldHaveType(DatetimeType::class);
     }
 
-    function it_should_return_valid_for_correct_values()
+    public function it_should_return_valid_for_correct_values(): void
     {
         $this->beConstructedWith('d-m-Y h:m:s', 'Europe/Berlin');
 
-        $this->check('12-12-2012 12:12:10')->isValid()->shouldBe(true);
+        $this->check('', '12-12-2012 12:12:10')->isValid()->shouldBe(true);
     }
 
-    function it_should_return_invalid_for_others()
+    public function it_should_return_invalid_for_others(): void
     {
         $this->beConstructedWith('d-m-Y h:m:s', 'Europe/Berlin');
 
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check('foo')->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1.234)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 'foo')->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1.234)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/EnumTypeSpec.php b/spec/Type/EnumTypeSpec.php
new file mode 100644
index 0000000..453c4e1
--- /dev/null
+++ b/spec/Type/EnumTypeSpec.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\EnumType;
+use PhpSpec\ObjectBehavior;
+
+class EnumTypeSpec extends ObjectBehavior
+{
+    function it_is_initializable()
+    {
+        $this->beConstructedWith(['test', 1, null]);
+
+        $this->shouldHaveType(EnumType::class);
+    }
+
+    function it_is_valid_for_all_allowed_values()
+    {
+        $this->beConstructedWith(['test', 1, null]);
+
+        $this->check('', 'test')->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
+    }
+
+    function it_is_invalid_for_not_allowed_values()
+    {
+        $this->beConstructedWith(['test', 1, null]);
+
+        $this->check('', 'array')->isValid()->shouldBe(false);
+        $this->check('', 100)->isValid()->shouldBe(false);
+        $this->check('', 1.5)->isValid()->shouldBe(false);
+        $this->check('', ['test'])->isValid()->shouldBe(false);
+    }
+}
diff --git a/spec/Type/ExactValueTypeSpec.php b/spec/Type/ExactValueTypeSpec.php
index 38ff88b..c2faf8b 100644
--- a/spec/Type/ExactValueTypeSpec.php
+++ b/spec/Type/ExactValueTypeSpec.php
@@ -1,8 +1,10 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\ExactValueType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\ExactValueType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
@@ -17,6 +19,6 @@ function it_is_initializable()
     function it_is_valid_for_null_if_null_is_the_value()
     {
         $this->beConstructedWith(null);
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 }
diff --git a/spec/Type/FloatTypeSpec.php b/spec/Type/FloatTypeSpec.php
index 04e1dd3..698abf6 100644
--- a/spec/Type/FloatTypeSpec.php
+++ b/spec/Type/FloatTypeSpec.php
@@ -1,8 +1,10 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\FloatType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\FloatType;
 use PhpSpec\ObjectBehavior;
 
 class FloatTypeSpec extends ObjectBehavior
@@ -14,19 +16,19 @@ function it_is_initializable()
 
     function it_should_return_valid_for_floats()
     {
-        $this->check(0.0)->isValid()->shouldBe(true);
-        $this->check(1.1)->isValid()->shouldBe(true);
-        $this->check(2.0)->isValid()->shouldBe(true);
-        $this->check(-144.2)->isValid()->shouldBe(true);
+        $this->check('', 0.0)->isValid()->shouldBe(true);
+        $this->check('', 1.1)->isValid()->shouldBe(true);
+        $this->check('', 2.0)->isValid()->shouldBe(true);
+        $this->check('', -144.2)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/IntTypeSpec.php b/spec/Type/IntTypeSpec.php
index df75166..93bc2b7 100644
--- a/spec/Type/IntTypeSpec.php
+++ b/spec/Type/IntTypeSpec.php
@@ -1,8 +1,10 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\IntType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\IntType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
@@ -15,19 +17,19 @@ function it_is_initializable()
 
     function it_should_return_valid_for_integers()
     {
-        $this->check(0)->isValid()->shouldBe(true);
-        $this->check(1)->isValid()->shouldBe(true);
-        $this->check(20)->isValid()->shouldBe(true);
-        $this->check(-144)->isValid()->shouldBe(true);
+        $this->check('', 0)->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', 20)->isValid()->shouldBe(true);
+        $this->check('', -144)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1.234)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1.234)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/ListTypeSpec.php b/spec/Type/ListTypeSpec.php
index 7884f1d..8edad91 100644
--- a/spec/Type/ListTypeSpec.php
+++ b/spec/Type/ListTypeSpec.php
@@ -1,11 +1,13 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\ListType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\ListType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class ListTypeSpec extends ObjectBehavior
 {
diff --git a/spec/Type/NullableTypeSpec.php b/spec/Type/NullableTypeSpec.php
index 54a092a..0a3ed46 100644
--- a/spec/Type/NullableTypeSpec.php
+++ b/spec/Type/NullableTypeSpec.php
@@ -1,11 +1,13 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\Type\NullableType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\Type\NullableType;
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class NullableTypeSpec extends ObjectBehavior
 {
@@ -17,12 +19,12 @@ function it_is_initializable(TypeInterface $childType)
 
     function it_should_return_valid_for_null(TypeInterface $childType) {
         $this->beConstructedWith($childType);
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 
     function it_should_return_the_value_from_the_child(TypeInterface $childType) {
         $this->beConstructedWith($childType);
-        $childType->check(false)->willReturn(new Result(false, []));
-        $this->check(false)->isValid()->shouldBe(false);
+        $childType->check('', false)->willReturn(new Result(false, []));
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/NumericTypeSpec.php b/spec/Type/NumericTypeSpec.php
index 9e863a3..449cbc2 100644
--- a/spec/Type/NumericTypeSpec.php
+++ b/spec/Type/NumericTypeSpec.php
@@ -1,8 +1,10 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\NumericType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\NumericType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
@@ -15,26 +17,26 @@ function it_is_initializable()
 
     function it_should_return_valid_for_integers()
     {
-        $this->check(0)->isValid()->shouldBe(true);
-        $this->check(1)->isValid()->shouldBe(true);
-        $this->check(20)->isValid()->shouldBe(true);
-        $this->check(-144)->isValid()->shouldBe(true);
+        $this->check('', 0)->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', 20)->isValid()->shouldBe(true);
+        $this->check('', -144)->isValid()->shouldBe(true);
     }
 
     function it_should_return_valid_for_floats()
     {
-        $this->check(0.0)->isValid()->shouldBe(true);
-        $this->check(1.1235)->isValid()->shouldBe(true);
-        $this->check(-0.00001)->isValid()->shouldBe(true);
-        $this->check(-144.12313131313)->isValid()->shouldBe(true);
+        $this->check('', 0.0)->isValid()->shouldBe(true);
+        $this->check('', 1.1235)->isValid()->shouldBe(true);
+        $this->check('', -0.00001)->isValid()->shouldBe(true);
+        $this->check('', -144.12313131313)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/ObjectTypeSpec.php b/spec/Type/ObjectTypeSpec.php
index 3b94d01..3941dde 100644
--- a/spec/Type/ObjectTypeSpec.php
+++ b/spec/Type/ObjectTypeSpec.php
@@ -1,11 +1,13 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\ObjectType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\ObjectType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class ObjectTypeSpec extends ObjectBehavior
 {
diff --git a/spec/Type/OptionalTypeSpec.php b/spec/Type/OptionalTypeSpec.php
index 7410167..f5611e2 100644
--- a/spec/Type/OptionalTypeSpec.php
+++ b/spec/Type/OptionalTypeSpec.php
@@ -1,23 +1,26 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\Type\OptionalType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\Type\OptionalType;
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
 class OptionalTypeSpec extends ObjectBehavior
 {
-    function it_is_initializable(TypeInterface $childType)
+    function it_is_initializable(TypeInterface $childType): void
     {
         $this->beConstructedWith($childType);
         $this->shouldHaveType(OptionalType::class);
     }
 
-    function it_should_return_the_value_from_the_child(TypeInterface $childType) {
+    function it_should_return_the_value_from_the_child(TypeInterface $childType): void
+    {
         $this->beConstructedWith($childType);
-        $childType->check(false)->willReturn(new Result(false, []));
-        $this->check(false)->isValid()->shouldBe(false);
+        $childType->check('', false)->willReturn(new Result(false, []));
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/RegexTypeSpec.php b/spec/Type/RegexTypeSpec.php
index 5b89312..3f260a4 100644
--- a/spec/Type/RegexTypeSpec.php
+++ b/spec/Type/RegexTypeSpec.php
@@ -1,42 +1,44 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
+
+namespace spec\Cubicl\StructureCheck\Type;
 
 use PhpSpec\ObjectBehavior;
-use StructureCheck\Type\RegexType;
+use Cubicl\StructureCheck\Type\RegexType;
 
 class RegexTypeSpec extends ObjectBehavior
 {
 
-    function it_is_initializable()
+    function it_is_initializable(): void
     {
         $this->beConstructedWith('/^def/');
 
         $this->shouldHaveType(RegexType::class);
     }
 
-    function it_should_return_valid_for_matching_strings()
+    function it_should_return_valid_for_matching_strings(): void
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check('definitive')->isValid()->shouldBe(true);
+        $this->check('', 'definitive')->isValid()->shouldBe(true);
     }
 
-    function it_should_return_invalid_for_not_matching_strings()
+    function it_should_return_invalid_for_not_matching_strings(): void
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check('developers')->isValid()->shouldBe(false);
+        $this->check('', 'developers')->isValid()->shouldBe(false);
     }
 
-    function it_should_return_invalid_for_others()
+    function it_should_return_invalid_for_others(): void
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check(12.3)->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(-1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 12.3)->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', -1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/StringTypeSpec.php b/spec/Type/StringTypeSpec.php
index 789627b..9c1ca8c 100644
--- a/spec/Type/StringTypeSpec.php
+++ b/spec/Type/StringTypeSpec.php
@@ -1,31 +1,33 @@
 <?php
 
-namespace spec\StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Type\StringType;
+namespace spec\Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Type\StringType;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
 class StringTypeSpec extends ObjectBehavior
 {
-    function it_is_initializable()
+    function it_is_initializable(): void
     {
         $this->shouldHaveType(StringType::class);
     }
 
-    function it_should_return_valid_for_strings()
+    function it_should_return_valid_for_strings(): void
     {
-        $this->check("")->isValid()->shouldBe(true);
-        $this->check("fooo")->isValid()->shouldBe(true);
-        $this->check('adadsad asd a')->isValid()->shouldBe(true);
+        $this->check('', '')->isValid()->shouldBe(true);
+        $this->check('', 'fooo')->isValid()->shouldBe(true);
+        $this->check('', 'adadsad asd a')->isValid()->shouldBe(true);
     }
 
-    function it_should_return_invalid_for_others()
+    function it_should_return_invalid_for_others(): void
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check(12.3)->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(-1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 12.3)->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', -1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
     }
 }
diff --git a/src/Check/CountCheck.php b/src/Check/CountCheck.php
index c640dde..6b629d6 100644
--- a/src/Check/CountCheck.php
+++ b/src/Check/CountCheck.php
@@ -1,74 +1,51 @@
 <?php
 
-namespace StructureCheck\Check;
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck\Check;
 
 use Countable;
-use StructureCheck\Result;
-use StructureCheck\Type\TypeInterface;
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class CountCheck
- * @package StructureCheck\Check
- */
 class CountCheck implements TypeInterface
 {
-    /**
-     * @var string
-     */
-    private static $countErrorMessage = 'The given countable %s has not the expected count %d.';
+    private static string $countErrorMessage = 'The given countable %s has not the expected count %d.';
 
-    /**
-     * @var string
-     */
-    private static $countableErrorMessage = 'The given value %s is not a countable';
+    private static string $countableErrorMessage = 'The given value %s is not a countable';
 
-    /**
-     * @var TypeInterface
-     */
-    private $child;
+    private TypeInterface $child;
 
-    /**
-     * @var int
-     */
-    private $count;
+    private int $count;
 
-    /**
-     * CountCheck constructor.
-     *
-     * @param TypeInterface $child
-     * @param int $count
-     */
-    public function __construct(TypeInterface $child, $count)
+    public function __construct(TypeInterface $child, int $count)
     {
         $this->child = $child;
         $this->count = $count;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        $result = $this->child->check($value);
+        $result = $this->child->check($key, $value);
 
         if (!$result->isValid()) {
             return $result;
         }
 
         if (!$value instanceof Countable) {
-            return new Result(
-                false,
-                [sprintf(self::$countableErrorMessage, json_encode($value))]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$countableErrorMessage, json_encode($value)))
+            ]);
         }
 
         if (count($value) !== $this->count) {
-            return new Result(
-                false,
-                [sprintf(self::$countErrorMessage, json_encode($value), $this->count)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$countErrorMessage, json_encode($value), $this->count))
+            ]);
         }
 
-        return new Result(true);
+        return Result::valid();
     }
 }
diff --git a/src/Check/NumericRangeCheck.php b/src/Check/NumericRangeCheck.php
index b14c5c2..ef3dc38 100644
--- a/src/Check/NumericRangeCheck.php
+++ b/src/Check/NumericRangeCheck.php
@@ -1,14 +1,14 @@
 <?php
 
-namespace StructureCheck\Check;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\Type\TypeInterface;
+namespace Cubicl\StructureCheck\Check;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class NumericRangeCheck
- * @package StructureCheck\Check
- */
 class NumericRangeCheck implements TypeInterface
 {
     /**
@@ -36,43 +36,33 @@ class NumericRangeCheck implements TypeInterface
      */
     private $upperBound;
 
-    /**
-     * @param TypeInterface $child
-     * @param int $upperBound
-     * @param int $lowerBound
-     */
-    public function __construct(TypeInterface $child, $upperBound, $lowerBound)
+    public function __construct(TypeInterface $child, int $upperBound, int $lowerBound)
     {
         $this->child = $child;
         $this->upperBound = $upperBound;
         $this->lowerBound = $lowerBound;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        $result = $this->child->check($value);
+        $result = $this->child->check($key, $value);
 
         if (!$result->isValid()) {
-           return $result;
+            return $result;
         }
 
         if ($this->lowerBound > $value) {
-            return new Result(
-                false,
-                [sprintf(self::$lowerBoundErrorMessage, $this->lowerBound, $value)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$lowerBoundErrorMessage, $this->lowerBound, $value))
+            ]);
         }
 
         if ($this->upperBound < $value) {
-            return new Result(
-                false,
-                [sprintf(self::$upperBoundErrorMessage, $this->upperBound, $value)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$upperBoundErrorMessage, $this->lowerBound, $value))
+            ]);
         }
 
-        return new Result(true);
+        return Result::valid();
     }
 }
diff --git a/src/Checker.php b/src/Checker.php
index 88b3f3d..9f06034 100644
--- a/src/Checker.php
+++ b/src/Checker.php
@@ -1,22 +1,15 @@
 <?php
 
-namespace StructureCheck;
+declare(strict_types=1);
 
-use StructureCheck\Type\TypeInterface;
+namespace Cubicl\StructureCheck;
+
+use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class Checker
- * @package StructureCheck
- */
 class Checker implements CheckerInterface
 {
-
-    /**
-     * @inheritdoc
-     */
-    public function fulfills($element, TypeInterface $requirement)
+    public function fulfills($element, TypeInterface $requirement): ResultInterface
     {
-        return $requirement->check($element);
+        return $requirement->check('', $element);
     }
-
-}
\ No newline at end of file
+}
diff --git a/src/CheckerInterface.php b/src/CheckerInterface.php
index 57a0605..e6ecc55 100644
--- a/src/CheckerInterface.php
+++ b/src/CheckerInterface.php
@@ -1,21 +1,15 @@
 <?php
 
-namespace StructureCheck;
+declare(strict_types=1);
 
-use StructureCheck\Type\TypeInterface;
+namespace Cubicl\StructureCheck;
+
+use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Interface CheckerInterface
- * @package StructureCheck
- */
 interface CheckerInterface
 {
-
     /**
      * @param mixed $element the element which should be tested
-     * @param TypeInterface $requirement
-     *
-     * @return ResultInterface
      */
-    public function fulfills($element, TypeInterface $requirement);
-}
\ No newline at end of file
+    public function fulfills($element, TypeInterface $requirement): ResultInterface;
+}
diff --git a/src/Error.php b/src/Error.php
new file mode 100644
index 0000000..8b78ea5
--- /dev/null
+++ b/src/Error.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck;
+
+class Error implements ErrorInterface
+{
+    private string $key;
+
+    private string $message;
+
+    public function __construct(string $key, string $message)
+    {
+        $this->key = $key;
+        $this->message = $message;
+    }
+
+    public function getKey(): string
+    {
+        return $this->key;
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+}
diff --git a/src/ErrorInterface.php b/src/ErrorInterface.php
new file mode 100644
index 0000000..6efb18a
--- /dev/null
+++ b/src/ErrorInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck;
+
+interface ErrorInterface
+{
+    public function getKey(): string;
+
+    public function getMessage(): string;
+}
diff --git a/src/Result.php b/src/Result.php
index a6fbd1c..288baa5 100644
--- a/src/Result.php
+++ b/src/Result.php
@@ -1,49 +1,47 @@
 <?php
 
-namespace StructureCheck;
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck;
 
-/**
- * Class Result
- * @package StructureCheck
- */
 class Result implements ResultInterface
 {
+    private bool $valid;
 
     /**
-     * @var bool
-     */
-    private $valid;
-
-    /**
-     * @var array
+     * @var array<ErrorInterface>
      */
-    private $errors;
+    private array $errors;
 
     /**
-     * Result constructor.
-     *
-     * @param bool $valid
-     * @param array $errors
+     * @param array<ErrorInterface> $errors
      */
-    public function __construct($valid, array $errors = [])
+    public function __construct(bool $valid, array $errors)
     {
         $this->valid = $valid;
         $this->errors = $errors;
     }
 
+    public static function valid(): ResultInterface
+    {
+        return new self(true, []);
+    }
+
     /**
-     * @inheritdoc
+     * @param array<ErrorInterface> $errors
      */
-    public function isValid()
+    public static function invalid(array $errors): ResultInterface
+    {
+        return new self(false, $errors);
+    }
+
+    public function isValid(): bool
     {
         return $this->valid;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function getErrors()
+    public function getErrors(): array
     {
         return $this->errors;
     }
-}
\ No newline at end of file
+}
diff --git a/src/ResultInterface.php b/src/ResultInterface.php
index 8a4ee76..17eabde 100644
--- a/src/ResultInterface.php
+++ b/src/ResultInterface.php
@@ -1,24 +1,23 @@
 <?php
 
-namespace StructureCheck;
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck;
 
 /**
- *
- * @package StructureCheck
+ * @package Cubicl\StructureCheck
  */
 interface ResultInterface
 {
     /**
      * Returns TRUE if the check was successful.
-     *
-     * @return bool
      */
-    public function isValid();
+    public function isValid(): bool;
 
     /**
      * Returns a list of errors. If no error occurred, it will return an empty array.
      *
-     * @return array
+     * @return array<ErrorInterface>
      */
-    public function getErrors();
-}
\ No newline at end of file
+    public function getErrors(): array;
+}
diff --git a/src/Type/AnyType.php b/src/Type/AnyType.php
index 4e8b1b4..aecd21b 100644
--- a/src/Type/AnyType.php
+++ b/src/Type/AnyType.php
@@ -1,20 +1,16 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class AnyType
- * @package StructureCheck\Type
- */
 class AnyType implements TypeInterface
 {
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        return new Result(true);
+        return Result::valid();
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/BoolType.php b/src/Type/BoolType.php
index 3c653d9..d935b29 100644
--- a/src/Type/BoolType.php
+++ b/src/Type/BoolType.php
@@ -1,30 +1,23 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class BoolType
- * @package StructureCheck\Type
- */
 class BoolType implements TypeInterface
 {
-    private static $errorMessage = 'The value %s is not a boolean.';
+    private static string $errorMessage = 'The value %s is not a boolean.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_bool($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/DatetimeType.php b/src/Type/DatetimeType.php
index 6271283..1bed289 100644
--- a/src/Type/DatetimeType.php
+++ b/src/Type/DatetimeType.php
@@ -1,69 +1,45 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
 use DateTime;
 use DateTimeZone;
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class DatetimeType
- * @package StructureCheck\Type
- */
-class DatetimeType
+class DatetimeType implements TypeInterface
 {
-    /**
-     * @var string
-     */
-    private static $errorMessage = 'The value %s is not a valid datetime.';
+    private static string $errorMessage = 'The value %s is not a valid datetime.';
 
-    /**
-     * @var string
-     */
-    private $datetimeFormat;
+    private string $datetimeFormat;
 
-    /**
-     * @var string
-     */
-    private $datetimeZone;
+    private string $datetimeZone;
 
-    /**
-     * DatetimeType constructor.
-     *
-     * @param string $format
-     * @param string $datetimeZone
-     */
-    public function __construct($format, $datetimeZone)
+    public function __construct(string $format, string $datetimeZone)
     {
         $this->datetimeFormat = $format;
         $this->datetimeZone = $datetimeZone;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value) && $this->isValidDatetime($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
 
-    /**
-     * @param string $value
-     *
-     * @return bool
-     */
-    private function isValidDatetime($value) {
+    private function isValidDatetime(string $value): bool
+    {
         $date = DateTime::createFromFormat($this->datetimeFormat, $value, new DateTimeZone($this->datetimeZone));
-        $errors = DateTime::getLastErrors()["warning_count"];
+        $errors = DateTime::getLastErrors();
 
-        return $date && $errors["warning_count"] == 0 && $errors["error_count"] == 0;
+        return $date && (
+            !$errors || ($errors['warning_count'] === 0 && $errors['error_count'] === 0)
+        );
     }
 }
diff --git a/src/Type/EnumType.php b/src/Type/EnumType.php
new file mode 100644
index 0000000..064e502
--- /dev/null
+++ b/src/Type/EnumType.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+
+/**
+ * @template T
+ */
+class EnumType implements TypeInterface
+{
+    private static string $errorMessage = 'The value %s is not in the allowed values (%s).';
+
+    /** @var array<T> */
+    private array $values;
+
+    /**
+     * @param array<T> $values
+     */
+    public function __construct(array $values)
+    {
+        $this->values = $values;
+    }
+
+    /**
+     * @param string $key
+     * @param T $value
+     */
+    public function check(string $key, $value): ResultInterface
+    {
+        $checkResult = in_array($value, $this->values, true);
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), implode(',', $this->values)))
+            ]);
+    }
+}
diff --git a/src/Type/ExactValueType.php b/src/Type/ExactValueType.php
index ae72087..36d03cb 100644
--- a/src/Type/ExactValueType.php
+++ b/src/Type/ExactValueType.php
@@ -1,21 +1,21 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
 
-class ExactValueType
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+
+class ExactValueType implements TypeInterface
 {
+    private static string $errorMessage = 'The value %s is not the same value as %s.';
 
-    /**
-     * @var string
-     */
-    private static $errorMessage = 'The value %s is not the same value as %s.';
+    /** @var mixed */
+    private $value;
 
     /**
-     * ExactValueType constructor.
-     *
      * @param mixed $value
      */
     public function __construct($value)
@@ -23,18 +23,14 @@ public function __construct($value)
         $this->value = $value;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = $this->value === $value;
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value), $this->value)] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), json_encode($this->value)))
+            ]);
     }
 }
diff --git a/src/Type/FloatType.php b/src/Type/FloatType.php
index 70e74b4..80aec7a 100644
--- a/src/Type/FloatType.php
+++ b/src/Type/FloatType.php
@@ -1,23 +1,23 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
 class FloatType implements TypeInterface
 {
-    private static $errorMessage = 'The value %s is not a float.';
+    private static string $errorMessage = 'The value %s is not a float.';
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_float($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/IntType.php b/src/Type/IntType.php
index 1cce655..9dd3f59 100644
--- a/src/Type/IntType.php
+++ b/src/Type/IntType.php
@@ -1,30 +1,23 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class IntType
- * @package StructureCheck\Type
- */
 class IntType implements TypeInterface
 {
-    private static $errorMessage = 'The value %s is not an integer.';
+    private static string $errorMessage = 'The value %s is not an integer.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_int($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/ListType.php b/src/Type/ListType.php
index cf1364e..4221461 100644
--- a/src/Type/ListType.php
+++ b/src/Type/ListType.php
@@ -1,54 +1,44 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class ListType
- * @package StructureCheck\Type
- */
 class ListType implements TypeInterface
 {
-    private static $isNotAnArrayMessage = 'The given value %s is not an array.';
-
-    /**
-     * @var TypeInterface[]
-     */
-    private $child;
-
-    /**
-     * ListType constructor.
-     *
-     * @param TypeInterface $child
-     */
+    private static string $isNotAnArrayMessage = 'The given value %s is not an array.';
+
+    private TypeInterface $child;
+
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         if (!is_array($value)) {
-            return new Result(
-                false,
-                [sprintf(self::$isNotAnArrayMessage, json_encode($value))]
+            return Result::invalid(
+                [new Error($key, sprintf(self::$isNotAnArrayMessage, json_encode($value)))]
             );
         }
 
         $errors = [];
         $valid = true;
 
-        foreach ($value as $item) {
-            $result = $this->child->check($item);
+        foreach ($value as $idx => $item) {
+            $result = $this->child->check(sprintf('%s.%d', $key, $idx), $item);
 
             $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }
 
-        return new Result($valid, $errors);
+        return $valid
+            ? Result::valid()
+            : Result::invalid($errors);
     }
 }
diff --git a/src/Type/NullableType.php b/src/Type/NullableType.php
index 8853ff9..f3eb64e 100644
--- a/src/Type/NullableType.php
+++ b/src/Type/NullableType.php
@@ -1,40 +1,27 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class NullableType
- * @package StructureCheck\Type
- */
 class NullableType implements TypeInterface
 {
+    private TypeInterface $child;
 
-    /**
-     * @var TypeInterface
-     */
-    private $child;
-
-    /**
-     * NullableType constructor.
-     *
-     * @param TypeInterface $child
-     */
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        if(is_null($value)) {
-            return new Result(true);
+        if ($value === null) {
+            return Result::valid();
         }
 
-        return $this->child->check($value);
+        return $this->child->check($key, $value);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/NumericType.php b/src/Type/NumericType.php
index 7cc1c56..96a24da 100644
--- a/src/Type/NumericType.php
+++ b/src/Type/NumericType.php
@@ -1,26 +1,23 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
 
-class NumericType
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+
+class NumericType implements TypeInterface
 {
-    private static $errorMessage = 'The value %s is not a numeric value.';
+    private static string $errorMessage = 'The value %s is not a numeric value.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_numeric($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
 }
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index cf8b371..35e9999 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -1,21 +1,21 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
 class ObjectType implements TypeInterface
 {
-    private static $missingKeyErrorMessage = 'The key "%s" does not exists';
+    private static string $missingKeyErrorMessage = 'The key "%s" does not exists';
 
-    /**
-     * @var TypeInterface[]
-     */
-    private $children;
+    /** @var TypeInterface[] */
+    private array $children;
 
     /**
-     * ObjectType constructor.
-     *
      * @param TypeInterface[] $children
      */
     public function __construct(array $children)
@@ -23,25 +23,22 @@ public function __construct(array $children)
         $this->children = $children;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $errors = [];
         $valid = true;
 
-        foreach ($this->children as $key => $child) {
-            if (!array_key_exists($key, $value)) {
+        foreach ($this->children as $objectProperty => $child) {
+            $fullKey = sprintf('%s.%s', $key, $objectProperty);
+            if (!array_key_exists($objectProperty, $value)) {
                 if (!$child instanceof OptionalType) {
                     $valid = false;
-                    $errors[] = sprintf(self::$missingKeyErrorMessage, $key);
+                    $errors[] = new Error($fullKey, sprintf(self::$missingKeyErrorMessage, $objectProperty));
                 }
-
                 continue;
             }
 
-            $result = $child->check($value[$key]);
+            $result = $child->check($fullKey, $value[$objectProperty]);
             $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }
diff --git a/src/Type/OptionalType.php b/src/Type/OptionalType.php
index 9110a5a..91cb0b8 100644
--- a/src/Type/OptionalType.php
+++ b/src/Type/OptionalType.php
@@ -1,37 +1,22 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class OptionalType
- * @package StructureCheck\Type
- * @author Christian Blank <christian@cubicl.de>
- */
 class OptionalType implements TypeInterface
 {
-    /**
-     * @var TypeInterface
-     */
-    private $child;
+    private TypeInterface $child;
 
-    /**
-     * OptionalType constructor.
-     * @param TypeInterface $child
-     */
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        return $this->child->check($value);
+        return $this->child->check($key, $value);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/RegexType.php b/src/Type/RegexType.php
index fe033c8..7471246 100644
--- a/src/Type/RegexType.php
+++ b/src/Type/RegexType.php
@@ -1,48 +1,32 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
 
-/**
- * Class RegexType
- * @package StructureCheck\Type
- */
-class RegexType
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
+
+class RegexType implements TypeInterface
 {
-    /**
-     * @var string
-     */
-    private static $errorMessage = 'The value %s does not match the regex %s';
-
-    /**
-     * @var string
-     */
-    private $regex;
-
-    /**
-     * RegexType constructor.
-     *
-     * @param string $regex
-     */
-    public function __construct($regex)
+    private static string $errorMessage = 'The value %s does not match the regex %s';
+
+    private string $regex;
+
+    public function __construct(string $regex)
     {
         $this->regex = $regex;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value) && preg_match($this->regex, $value) === 1;
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value), $this->regex)] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), json_encode($this->regex)))
+            ]);
     }
 }
diff --git a/src/Type/StringType.php b/src/Type/StringType.php
index 46af09d..7fcb4ca 100644
--- a/src/Type/StringType.php
+++ b/src/Type/StringType.php
@@ -1,30 +1,23 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\Result;
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\Error;
+use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class StringType
- * @package StructureCheck\Type
- */
 class StringType implements TypeInterface
 {
-    private static $errorMessage = 'The value %s is not a string.';
+    private static string $errorMessage = 'The value %s is not a string.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/TypeInterface.php b/src/Type/TypeInterface.php
index d544892..5c06b16 100644
--- a/src/Type/TypeInterface.php
+++ b/src/Type/TypeInterface.php
@@ -1,19 +1,15 @@
 <?php
 
-namespace StructureCheck\Type;
+declare(strict_types=1);
 
-use StructureCheck\ResultInterface;
+namespace Cubicl\StructureCheck\Type;
+
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Interface TypeInterface
- * @package StructureCheck\Type
- */
 interface TypeInterface
 {
     /**
      * @param mixed $value
-     *
-     * @return ResultInterface
      */
-    public function check($value);
-}
\ No newline at end of file
+    public function check(string $key, $value): ResultInterface;
+}
diff --git a/tests/Integration/Type/ObjectTypeTest.php b/tests/Integration/Type/ObjectTypeTest.php
index b2302e9..2028624 100644
--- a/tests/Integration/Type/ObjectTypeTest.php
+++ b/tests/Integration/Type/ObjectTypeTest.php
@@ -1,30 +1,26 @@
 <?php
 
-namespace StructureCheck\Test\Integration\Type;
+declare(strict_types=1);
+
+namespace Cubicl\StructureCheck\Test\Integration\Type;
 
 use PHPUnit\Framework\TestCase;
-use StructureCheck\Checker;
-use StructureCheck\CheckerInterface;
-use StructureCheck\Type\AnyType;
-use StructureCheck\Type\ObjectType;
-use StructureCheck\Type\OptionalType;
+use Cubicl\StructureCheck\Checker;
+use Cubicl\StructureCheck\CheckerInterface;
+use Cubicl\StructureCheck\Type\AnyType;
+use Cubicl\StructureCheck\Type\ObjectType;
+use Cubicl\StructureCheck\Type\OptionalType;
 
 /**
  * Class ObjectTypeTest
- * @package StructureCheck\Test\Integration\Type
+ * @package Cubicl\StructureCheck\Test\Integration\Type
  * @author Christian Blank <christian@cubicl.de>
  */
 class ObjectTypeTest extends TestCase
 {
-    /**
-     * @var CheckerInterface
-     */
-    private $checker;
+    private CheckerInterface $checker;
 
-    /**
-     *
-     */
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
         $this->checker = new Checker();
@@ -33,14 +29,14 @@ protected function setUp()
     /**
      * @test
      */
-    public function itShouldHandleAbsenceOfOptionalDeclaredType()
+    public function itShouldHandleAbsenceOfOptionalDeclaredType(): void
     {
         $structure = new ObjectType([
             'opt' => new OptionalType(new AnyType())
         ]);
 
-        $actual = $structure->check([]);
+        $actual = $structure->check('', []);
 
         $this->assertSame(true, $actual->isValid());
     }
-}
\ No newline at end of file
+}