Utilities
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.
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{Math}, {SignedMath}: Implementation of various arithmetic functions.
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{SafeCast}: Checked downcasting functions to avoid silent truncation.
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{ECDSA}, {MessageHashUtils}: Libraries for interacting with ECDSA signatures.
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{SignatureChecker}: A library helper to support regular ECDSA from EOAs as well as ERC-1271 signatures for smart contracts.
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{MerkleProof}: Functions for verifying Merkle Tree proofs.
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{EIP712}: Contract with functions to allow processing signed typed structure data according to EIP-712.
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{ReentrancyGuard}: A modifier that can prevent reentrancy during certain functions.
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{Pausable}: A common emergency response mechanism that can pause functionality while a remediation is pending.
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{Nonces}: Utility for tracking and verifying address nonces that only increment.
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{ERC165, ERC165Checker}: Utilities for inspecting interfaces supported by contracts.
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{BitMaps}: A simple library to manage boolean value mapped to a numerical index in an efficient way.
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{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 withmapping
). -
{EnumerableSet}: Like {EnumerableMap}, but for sets. Can be used to store privileged accounts, issued IDs, etc.
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{DoubleEndedQueue}: An implementation of a double ended queue whose values can be removed added or remove from both sides. Useful for FIFO and LIFO structures.
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{Checkpoints}: A data structure to store values mapped to an strictly increasing key. Can be used for storing and accessing values over time.
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{Create2}: Wrapper around the
CREATE2
EVM opcode for safe use without having to deal with low-level assembly. -
{Address}: Collection of functions for overloading Solidity’s
address
type. -
{Arrays}: Collection of functions that operate on
arrays
. -
{Base64}: On-chain base64 and base64URL encoding according to RFC-4648.
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{Strings}: Common operations for strings formatting.
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{ShortString}: Library to encode (and decode) short strings into (or from) a single bytes32 slot for optimizing costs. Short strings are limited to 31 characters.
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{StorageSlot}: Methods for accessing specific storage slots formatted as common primitive types.
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{Multicall}: Abstract contract with an utility to allow batching together multiple calls in a single transaction. Useful for allowing EOAs to perform multiple operations at once.
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{Context}: An utility for abstracting the sender and calldata in the current execution context.
Because Solidity does not support generic types, {EnumerableMap} and {EnumerableSet} are specialized to a limited number of key-value types. |
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. ERC20
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}}