Utilities

Note	This document is better viewed at https://docs.openzeppelin.com/contracts/api/utils

Miscellaneous contracts and libraries containing utility functions you can use to improve security, work with new data types, or safely use low-level primitives.

• {ReentrancyGuard}: A modifier that can prevent reentrancy during certain functions.

• {Pausable}: A common emergency response mechanism that can pause functionality while a remediation is pending.

• {SafeCast}: Checked downcasting functions to avoid silent truncation.

• {Math}, {SignedMath}: Implementation of various arithmetic functions.

• {Multicall}: Simple way to batch together multiple calls in a single external call.

• {Create2}: Wrapper around the CREATE2 EVM opcode for safe use without having to deal with low-level assembly.

• {EnumerableMap}: A type like Solidity’s mapping, but with key-value enumeration: this will let you know how many entries a mapping has, and iterate over them (which is not possible with mapping).

• {EnumerableSet}: Like {EnumerableMap}, but for sets. Can be used to store privileged accounts, issued IDs, etc.

Note	Because Solidity does not support generic types, {EnumerableMap} and {EnumerableSet} are specialized to a limited number of key-value types.

Math

{{Math}}

{{SignedMath}}

{{SafeCast}}

Cryptography

{{ECDSA}}

{{MessageHashUtils}}

{{SignatureChecker}}

{{MerkleProof}}

{{EIP712}}

Security

{{ReentrancyGuard}}

{{Pausable}}

Introspection

This set of interfaces and contracts deal with type introspection of contracts, that is, examining which functions can be called on them. This is usually referred to as a contract’s interface.

Ethereum contracts have no native concept of an interface, so applications must usually simply trust they are not making an incorrect call. For trusted setups this is a non-issue, but often unknown and untrusted third-party addresses need to be interacted with. There may even not be any direct calls to them! (e.g. ERC-20 tokens may be sent to a contract that lacks a way to transfer them out of it, locking them forever). In these cases, a contract declaring its interface can be very helpful in preventing errors.

{{IERC165}}

{{ERC165}}

{{ERC165Checker}}

Data Structures

{{BitMaps}}

{{EnumerableMap}}

{{EnumerableSet}}

{{DoubleEndedQueue}}

{{Checkpoints}}

Libraries

{{Create2}}

{{Address}}

{{Arrays}}

{{Base64}}

{{Strings}}

{{ShortStrings}}

{{StorageSlot}}

{{Multicall}}