Add .net standard 1.4 target to Microsoft.Toolkit project.

Microsoft.Toolkit/Diagnostics/Guard.cs

@@ -6,6 +6,9 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
+#if NETSTANDARD1_4
+using Microsoft.Toolkit.Extensions;
+#endif
 
 #nullable enable
 

Microsoft.Toolkit/Extensions/TypeExtensions.cs

@@ -6,6 +6,9 @@
 using System.Collections.Generic;
 using System.Diagnostics.Contracts;
 using System.Linq;
+#if NETSTANDARD1_4
+using System.Reflection;
+#endif
 using System.Runtime.CompilerServices;
 
 #nullable enable
@@ -62,7 +65,12 @@ static string FormatDisplayString(Type type)
                 }
 
                 // Generic types
-                if (type.IsGenericType &&
+                if (
+#if NETSTANDARD1_4
+                    type.GetTypeInfo().IsGenericType &&
+#else
+                    type.IsGenericType &&
+#endif
                     type.FullName is { } fullName &&
                     fullName.Split('`') is { } tokens &&
                     tokens.Length > 0 &&
@@ -113,5 +121,28 @@ tokens[0] is { } genericName &&
             // be removed once this issue is resolved: https://github.com/dotnet/roslyn/issues/5835.
             return DisplayNames.GetValue(type, t => FormatDisplayString(t));
         }
+
+#if NETSTANDARD1_4
+        /// <summary>
+        /// Returns an array of types representing the generic arguments.
+        /// </summary>
+        /// <param name="type">The input type.</param>
+        /// <returns>An array of types representing the generic arguments.</returns>
+        private static Type[] GetGenericArguments(this Type type)
+        {
+            return type.GetTypeInfo().GenericTypeParameters;
+        }
+
+        /// <summary>
+        /// Returns whether <paramref name="type"/> is an instance of <paramref name="value"/>.
+        /// </summary>
+        /// <param name="type">The input type.</param>
+        /// <param name="value">The type to check against.</param>
+        /// <returns><see langword="true"/> if <paramref name="type"/> is an instance of <paramref name="value"/>, <see langword="false"/> otherwise.</returns>
+        internal static bool IsInstanceOfType(this Type type, object value)
+        {
+            return type.GetTypeInfo().IsAssignableFrom(value.GetType().GetTypeInfo());
+        }
+#endif
     }
 }

Microsoft.Toolkit/Microsoft.Toolkit.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard1.4;netstandard2.0;netstandard2.1</TargetFrameworks>
     <LangVersion>8.0</LangVersion>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Title>Windows Community Toolkit .NET Standard</Title>
@@ -13,6 +13,13 @@
     <PackageTags>UWP Toolkit Windows IncrementalLoadingCollection String Array extensions helpers</PackageTags>
   </PropertyGroup>
 
+  <!-- .NET Standard 1.4 doesn't have the Span<T> type, ValueTuple or the [Pure] attribute -->
+  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.4' ">
+    <PackageReference Include="System.Diagnostics.Contracts" Version="4.3.0" />
+    <PackageReference Include="System.ValueTuple" Version="4.5.0" />
+    <PackageReference Include="System.Memory" Version="4.5.4" />
+  </ItemGroup>
+
   <!-- .NET Standard 2.0 doesn't have the Span<T> type -->
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="System.Memory" Version="4.5.4" />
@@ -70,4 +77,4 @@
     </Compile>
   </ItemGroup>
 
-</Project>
+</Project>