solidity/docs/cheatsheet.rst

**********
Cheatsheet
**********

.. index:: operator; precedence

Order of Precedence of Operators
================================
.. include:: types/operator-precedence-table.rst

.. index:: assert, block, coinbase, difficulty, number, block;number, timestamp, block;timestamp, msg, data, gas, sender, value, gas price, origin, revert, require, keccak256, ripemd160, sha256, ecrecover, addmod, mulmod, cryptography, this, super, selfdestruct, balance, codehash, send

Global Variables
================

- ``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)), ...)``
- ``bytes.concat(...) returns (bytes memory)``: :ref:`Concatenates variable number of
  arguments to one byte array<bytes-concat>`
- ``string.concat(...) returns (string memory)``: :ref:`Concatenates variable number of
  arguments to one string array<string-concat>`
- ``block.basefee`` (``uint``): current block's base fee (`EIP-3198 <https://eips.ethereum.org/EIPS/eip-3198>`_ and `EIP-1559 <https://eips.ethereum.org/EIPS/eip-1559>`_)
- ``block.chainid`` (``uint``): current chain id
- ``block.coinbase`` (``address payable``): current block miner's address
- ``block.difficulty`` (``uint``): current block difficulty
- ``block.gaslimit`` (``uint``): current block gaslimit
- ``block.number`` (``uint``): current block number
- ``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)
- ``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
- ``blockhash(uint blockNumber) returns (bytes32)``: hash of the given block - only works for 256 most recent blocks
- ``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.
- ``this`` (current contract's type): the current contract, explicitly convertible to ``address`` or ``address payable``
- ``super``: the contract one level higher in the inheritance hierarchy
- ``selfdestruct(address payable recipient)``: destroy the current contract, sending its funds to the given 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
- ``type(C).name`` (``string``): the name of the contract
- ``type(C).creationCode`` (``bytes memory``): creation bytecode of the given contract, see :ref:`Type Information<meta-type>`.
- ``type(C).runtimeCode`` (``bytes memory``): runtime bytecode of the given contract, see :ref:`Type Information<meta-type>`.
- ``type(I).interfaceId`` (``bytes4``): value containing the EIP-165 interface identifier of the given interface, see :ref:`Type Information<meta-type>`.
- ``type(T).min`` (``T``): the minimum value representable by the integer type ``T``, see :ref:`Type Information<meta-type>`.
- ``type(T).max`` (``T``): the maximum value representable by the integer type ``T``, see :ref:`Type Information<meta-type>`.


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

Function Visibility Specifiers
==============================

.. code-block:: solidity
    :force:

    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.