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Cheatsheet

.. index:: operator;precedence

Order of Precedence of Operators

.. index:: abi;decode, abi;encode, abi;encodePacked, abi;encodeWithSelector, abi;encodeCall, abi;encodeWithSignature

ABI Encoding and Decoding Functions

  • abi.decode(bytes memory encodedData, (...)) returns (...): :ref:`ABI <ABI>`-decodes the provided data. The types are given in parentheses as second argument. Example: (uint a, uint[2] memory b, bytes memory c) = abi.decode(data, (uint, uint[2], bytes))
  • abi.encode(...) returns (bytes memory): :ref:`ABI <ABI>`-encodes the given arguments
  • abi.encodePacked(...) returns (bytes memory): Performs :ref:`packed encoding <abi_packed_mode>` of the given arguments. Note that this encoding can be ambiguous!
  • abi.encodeWithSelector(bytes4 selector, ...) returns (bytes memory): :ref:`ABI <ABI>`-encodes the given arguments starting from the second and prepends the given four-byte selector
  • abi.encodeCall(function functionPointer, (...)) returns (bytes memory): ABI-encodes a call to functionPointer with the arguments found in the tuple. Performs a full type-check, ensuring the types match the function signature. Result equals abi.encodeWithSelector(functionPointer.selector, (...))
  • abi.encodeWithSignature(string memory signature, ...) returns (bytes memory): Equivalent to abi.encodeWithSelector(bytes4(keccak256(bytes(signature))), ...)
.. index:: bytes;concat, string;concat

Members of bytes and string

.. index:: address;balance, address;codehash, address;send, address;code, address;transfer

Members of address

  • <address>.balance (uint256): balance of the :ref:`address` in Wei
  • <address>.code (bytes memory): code at the :ref:`address` (can be empty)
  • <address>.codehash (bytes32): the codehash of the :ref:`address`
  • <address payable>.send(uint256 amount) returns (bool): send given amount of Wei to :ref:`address`, returns false on failure
  • <address payable>.transfer(uint256 amount): send given amount of Wei to :ref:`address`, throws on failure
.. index:: blockhash, block, block;basefree, block;chainid, block;coinbase, block;difficulty, block;gaslimit, block;number, block;prevrandao, block;timestamp

.. index:: gasleft, msg;data, msg;sender, msg;sig, msg;value, tx;gasprice, tx;origin

Block and Transaction Properties

  • blockhash(uint blockNumber) returns (bytes32): hash of the given block - only works for 256 most recent blocks
  • block.basefee (uint): current block's base fee (EIP-3198 and EIP-1559)
  • block.chainid (uint): current chain id
  • block.coinbase (address payable): current block miner's address
  • block.difficulty (uint): current block difficulty (EVM < Paris). For other EVM versions it behaves as a deprecated alias for block.prevrandao that will be removed in the next breaking release
  • block.gaslimit (uint): current block gaslimit
  • block.number (uint): current block number
  • block.prevrandao (uint): random number provided by the beacon chain (EVM >= Paris) (see EIP-4399 )
  • block.timestamp (uint): current block timestamp in seconds since Unix epoch
  • gasleft() returns (uint256): remaining gas
  • msg.data (bytes): complete calldata
  • msg.sender (address): sender of the message (current call)
  • msg.sig (bytes4): first four bytes of the calldata (i.e. function identifier)
  • msg.value (uint): number of wei sent with the message
  • tx.gasprice (uint): gas price of the transaction
  • tx.origin (address): sender of the transaction (full call chain)
.. index:: assert, require, revert

Validations and Assertions

  • assert(bool condition): abort execution and revert state changes if condition is false (use for internal error)
  • require(bool condition): abort execution and revert state changes if condition is false (use for malformed input or error in external component)
  • require(bool condition, string memory message): abort execution and revert state changes if condition is false (use for malformed input or error in external component). Also provide error message.
  • revert(): abort execution and revert state changes
  • revert(string memory message): abort execution and revert state changes providing an explanatory string
.. index:: cryptography, keccak256, sha256, ripemd160, ecrecover, addmod, mulmod

Mathematical and Cryptographic Functions

  • keccak256(bytes memory) returns (bytes32): compute the Keccak-256 hash of the input
  • sha256(bytes memory) returns (bytes32): compute the SHA-256 hash of the input
  • ripemd160(bytes memory) returns (bytes20): compute the RIPEMD-160 hash of the input
  • ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address): recover address associated with the public key from elliptic curve signature, return zero on error
  • addmod(uint x, uint y, uint k) returns (uint): compute (x + y) % k where the addition is performed with arbitrary precision and does not wrap around at 2**256. Assert that k != 0 starting from version 0.5.0.
  • mulmod(uint x, uint y, uint k) returns (uint): compute (x * y) % k where the multiplication is performed with arbitrary precision and does not wrap around at 2**256. Assert that k != 0 starting from version 0.5.0.
.. index:: this, super, selfdestruct

Contract-related

  • this (current contract's type): the current contract, explicitly convertible to address or address payable
  • super: a contract one level higher in the inheritance hierarchy
  • selfdestruct(address payable recipient): destroy the current contract, sending its funds to the given address
.. index:: type;name, type;creationCode, type;runtimeCode, type;interfaceId, type;min, type;max

Type Information

.. index:: visibility, public, private, external, internal

Function Visibility Specifiers

function myFunction() <visibility specifier> returns (bool) {
    return true;
}
  • public: visible externally and internally (creates a :ref:`getter function<getter-functions>` for storage/state variables)
  • private: only visible in the current contract
  • external: only visible externally (only for functions) - i.e. can only be message-called (via this.func)
  • internal: only visible internally
.. index:: modifiers, pure, view, payable, constant, anonymous, indexed

Modifiers

  • pure for functions: Disallows modification or access of state.
  • view for functions: Disallows modification of state.
  • payable for functions: Allows them to receive Ether together with a call.
  • constant for state variables: Disallows assignment (except initialisation), does not occupy storage slot.
  • immutable for state variables: Allows exactly one assignment at construction time and is constant afterwards. Is stored in code.
  • anonymous for events: Does not store event signature as topic.
  • indexed for event parameters: Stores the parameter as topic.
  • virtual for functions and modifiers: Allows the function's or modifier's behaviour to be changed in derived contracts.
  • override: States that this function, modifier or public state variable changes the behaviour of a function or modifier in a base contract.