********** Cheatsheet ********** .. index:: operator;precedence Order of Precedence of Operators ================================ .. include:: types/operator-precedence-table.rst .. 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 `-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 `-encodes the given arguments - ``abi.encodePacked(...) returns (bytes memory)``: Performs :ref:`packed encoding ` of the given arguments. Note that this encoding can be ambiguous! - ``abi.encodeWithSelector(bytes4 selector, ...) returns (bytes memory)``: :ref:`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`` ==================================== - ``bytes.concat(...) returns (bytes memory)``: :ref:`Concatenates variable number of arguments to one byte array` - ``string.concat(...) returns (string memory)``: :ref:`Concatenates variable number of arguments to one string array` .. index:: address;balance, address;codehash, address;send, address;code, address;transfer Members of ``address`` ====================== - ``
.balance`` (``uint256``): balance of the :ref:`address` in Wei - ``
.code`` (``bytes memory``): code at the :ref:`address` (can be empty) - ``
.codehash`` (``bytes32``): the codehash of the :ref:`address` - ``
.send(uint256 amount) returns (bool)``: send given amount of Wei to :ref:`address`, returns ``false`` on failure - ``
.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 ================ - ``type(C).name`` (``string``): the name of the contract - ``type(C).creationCode`` (``bytes memory``): creation bytecode of the given contract, see :ref:`Type Information`. - ``type(C).runtimeCode`` (``bytes memory``): runtime bytecode of the given contract, see :ref:`Type Information`. - ``type(I).interfaceId`` (``bytes4``): value containing the EIP-165 interface identifier of the given interface, see :ref:`Type Information`. - ``type(T).min`` (``T``): the minimum value representable by the integer type ``T``, see :ref:`Type Information`. - ``type(T).max`` (``T``): the maximum value representable by the integer type ``T``, see :ref:`Type Information`. .. index:: visibility, public, private, external, internal Function Visibility Specifiers ============================== .. code-block:: solidity :force: function myFunction() returns (bool) { return true; } - ``public``: visible externally and internally (creates a :ref:`getter function` 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 assignment at construction time and is constant when deployed. 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 behavior to be changed in derived contracts. - ``override``: States that this function, modifier or public state variable changes the behavior of a function or modifier in a base contract.