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

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

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

• {ECDSA}, {MessageHashUtils}: Libraries for interacting with ECDSA signatures.

• {SignatureChecker}: A library helper to support regular ECDSA from EOAs as well as ERC-1271 signatures for smart contracts.

• {MerkleProof}: Functions for verifying Merkle Tree proofs.

• {EIP712}: Contract with functions to allow processing signed typed structure data according to EIP-712.

• {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.

• {Nonces}: Utility for tracking and verifying address nonces that only increment.

• {ERC165, ERC165Checker}: Utilities for inspecting interfaces supported by contracts.

• {BitMaps}: A simple library to manage boolean value mapped to a numerical index in an efficient way.

• {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.

• {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.

• {Checkpoints}: A data structure to store values mapped to an strictly increasing key. Can be used for storing and accessing values over time.

• {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.

• {Strings}: Common operations for strings formatting.

• {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.

• {StorageSlot}: Methods for accessing specific storage slots formatted as common primitive types.

• {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.

• {Context}: An utility for abstracting the sender and calldata in the current execution context.

{{Math}}

{{SignedMath}}

{{SafeCast}}

{{ECDSA}}

{{MessageHashUtils}}

{{SignatureChecker}}

{{MerkleProof}}

{{EIP712}}

{{ReentrancyGuard}}

{{Pausable}}

{{Nonces}}

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}}

{{BitMaps}}

{{EnumerableMap}}

{{EnumerableSet}}

{{DoubleEndedQueue}}

{{Checkpoints}}

{{Create2}}

{{Address}}

{{Arrays}}

{{Base64}}

{{Strings}}

{{ShortStrings}}

{{StorageSlot}}

{{Multicall}}

{{Context}}