mirror of
https://github.com/ethereum/solidity
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200 lines
14 KiB
ReStructuredText
200 lines
14 KiB
ReStructuredText
**********
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Cheatsheet
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**********
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.. index:: precedence
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.. _order:
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Order of Precedence of Operators
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================================
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The following is the order of precedence for operators, listed in order of evaluation.
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+------------+-------------------------------------+--------------------------------------------+
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| Precedence | Description | Operator |
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+============+=====================================+============================================+
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| *1* | Postfix increment and decrement | ``++``, ``--`` |
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+ +-------------------------------------+--------------------------------------------+
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| | New expression | ``new <typename>`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Array subscripting | ``<array>[<index>]`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Member access | ``<object>.<member>`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Function-like call | ``<func>(<args...>)`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Parentheses | ``(<statement>)`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *2* | Prefix increment and decrement | ``++``, ``--`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Unary minus | ``-`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Unary operations | ``delete`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Logical NOT | ``!`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Bitwise NOT | ``~`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *3* | Exponentiation | ``**`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *4* | Multiplication, division and modulo | ``*``, ``/``, ``%`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *5* | Addition and subtraction | ``+``, ``-`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *6* | Bitwise shift operators | ``<<``, ``>>`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *7* | Bitwise AND | ``&`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *8* | Bitwise XOR | ``^`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *9* | Bitwise OR | ``|`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *10* | Inequality operators | ``<``, ``>``, ``<=``, ``>=`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *11* | Equality operators | ``==``, ``!=`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *12* | Logical AND | ``&&`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *13* | Logical OR | ``||`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *14* | Ternary operator | ``<conditional> ? <if-true> : <if-false>`` |
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+ +-------------------------------------+--------------------------------------------+
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| | Assignment operators | ``=``, ``|=``, ``^=``, ``&=``, ``<<=``, |
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| | | ``>>=``, ``+=``, ``-=``, ``*=``, ``/=``, |
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| | | ``%=`` |
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+------------+-------------------------------------+--------------------------------------------+
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| *15* | Comma operator | ``,`` |
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+------------+-------------------------------------+--------------------------------------------+
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.. 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
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Global Variables
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================
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- ``abi.decode(bytes memory encodedData, (...)) returns (...)``: :ref:`ABI <ABI>`-decodes
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the provided data. The types are given in parentheses as second argument.
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Example: ``(uint a, uint[2] memory b, bytes memory c) = abi.decode(data, (uint, uint[2], bytes))``
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- ``abi.encode(...) returns (bytes memory)``: :ref:`ABI <ABI>`-encodes the given arguments
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- ``abi.encodePacked(...) returns (bytes memory)``: Performs :ref:`packed encoding <abi_packed_mode>` of
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the given arguments. Note that this encoding can be ambiguous!
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- ``abi.encodeWithSelector(bytes4 selector, ...) returns (bytes memory)``: :ref:`ABI <ABI>`-encodes
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the given arguments starting from the second and prepends the given four-byte selector
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- ``abi.encodeWithSignature(string memory signature, ...) returns (bytes memory)``: Equivalent
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to ``abi.encodeWithSelector(bytes4(keccak256(bytes(signature)), ...)```
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- ``bytes.concat(...) returns (bytes memory)``: :ref:`Concatenates variable number of
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arguments to one byte array<bytes-concat>`
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- ``block.chainid`` (``uint``): current chain id
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- ``block.coinbase`` (``address payable``): current block miner's address
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- ``block.difficulty`` (``uint``): current block difficulty
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- ``block.gaslimit`` (``uint``): current block gaslimit
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- ``block.number`` (``uint``): current block number
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- ``block.timestamp`` (``uint``): current block timestamp
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- ``gasleft() returns (uint256)``: remaining gas
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- ``msg.data`` (``bytes``): complete calldata
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- ``msg.sender`` (``address``): sender of the message (current call)
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- ``msg.value`` (``uint``): number of wei sent with the message
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- ``tx.gasprice`` (``uint``): gas price of the transaction
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- ``tx.origin`` (``address``): sender of the transaction (full call chain)
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- ``assert(bool condition)``: abort execution and revert state changes if condition is ``false`` (use for internal error)
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- ``require(bool condition)``: abort execution and revert state changes if condition is ``false`` (use
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for malformed input or error in external component)
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- ``require(bool condition, string memory message)``: abort execution and revert state changes if
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condition is ``false`` (use for malformed input or error in external component). Also provide error message.
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- ``revert()``: abort execution and revert state changes
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- ``revert(string memory message)``: abort execution and revert state changes providing an explanatory string
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- ``blockhash(uint blockNumber) returns (bytes32)``: hash of the given block - only works for 256 most recent blocks
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- ``keccak256(bytes memory) returns (bytes32)``: compute the Keccak-256 hash of the input
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- ``sha256(bytes memory) returns (bytes32)``: compute the SHA-256 hash of the input
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- ``ripemd160(bytes memory) returns (bytes20)``: compute the RIPEMD-160 hash of the input
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- ``ecrecover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) returns (address)``: recover address associated with
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the public key from elliptic curve signature, return zero on error
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- ``addmod(uint x, uint y, uint k) returns (uint)``: compute ``(x + y) % k`` where the addition is performed with
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arbitrary precision and does not wrap around at ``2**256``. Assert that ``k != 0`` starting from version 0.5.0.
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- ``mulmod(uint x, uint y, uint k) returns (uint)``: compute ``(x * y) % k`` where the multiplication is performed
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with arbitrary precision and does not wrap around at ``2**256``. Assert that ``k != 0`` starting from version 0.5.0.
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- ``this`` (current contract's type): the current contract, explicitly convertible to ``address`` or ``address payable``
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- ``super``: the contract one level higher in the inheritance hierarchy
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- ``selfdestruct(address payable recipient)``: destroy the current contract, sending its funds to the given address
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- ``<address>.balance`` (``uint256``): balance of the :ref:`address` in Wei
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- ``<address>.code`` (``bytes memory``): code at the :ref:`address` (can be empty)
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- ``<address>.codehash`` (``bytes32``): the codehash of the :ref:`address`
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- ``<address payable>.send(uint256 amount) returns (bool)``: send given amount of Wei to :ref:`address`,
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returns ``false`` on failure
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- ``<address payable>.transfer(uint256 amount)``: send given amount of Wei to :ref:`address`, throws on failure
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- ``type(C).name`` (``string``): the name of the contract
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- ``type(C).creationCode`` (``bytes memory``): creation bytecode of the given contract, see :ref:`Type Information<meta-type>`.
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- ``type(C).runtimeCode`` (``bytes memory``): runtime bytecode of the given contract, see :ref:`Type Information<meta-type>`.
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- ``type(I).interfaceId`` (``bytes4``): value containing the EIP-165 interface identifier of the given interface, see :ref:`Type Information<meta-type>`.
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- ``type(T).min`` (``T``): the minimum value representable by the integer type ``T``, see :ref:`Type Information<meta-type>`.
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- ``type(T).max`` (``T``): the maximum value representable by the integer type ``T``, see :ref:`Type Information<meta-type>`.
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.. note::
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Do not rely on ``block.timestamp`` or ``blockhash`` as a source of randomness,
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unless you know what you are doing.
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Both the timestamp and the block hash can be influenced by miners to some degree.
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Bad actors in the mining community can for example run a casino payout function on a chosen hash
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and just retry a different hash if they did not receive any money.
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The current block timestamp must be strictly larger than the timestamp of the last block,
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but the only guarantee is that it will be somewhere between the timestamps of two
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consecutive blocks in the canonical chain.
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.. note::
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The block hashes are not available for all blocks for scalability reasons.
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You can only access the hashes of the most recent 256 blocks, all other
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values will be zero.
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.. note::
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In version 0.5.0, the following aliases were removed: ``suicide`` as alias for ``selfdestruct``,
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``msg.gas`` as alias for ``gasleft``, ``block.blockhash`` as alias for ``blockhash`` and
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``sha3`` as alias for ``keccak256``.
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.. note::
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In version 0.7.0, the alias ``now`` (for ``block.timestamp``) was removed.
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.. index:: visibility, public, private, external, internal
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Function Visibility Specifiers
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==============================
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::
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function myFunction() <visibility specifier> returns (bool) {
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return true;
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}
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- ``public``: visible externally and internally (creates a :ref:`getter function<getter-functions>` for storage/state variables)
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- ``private``: only visible in the current contract
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- ``external``: only visible externally (only for functions) - i.e. can only be message-called (via ``this.func``)
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- ``internal``: only visible internally
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.. index:: modifiers, pure, view, payable, constant, anonymous, indexed
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Modifiers
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=========
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- ``pure`` for functions: Disallows modification or access of state.
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- ``view`` for functions: Disallows modification of state.
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- ``payable`` for functions: Allows them to receive Ether together with a call.
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- ``constant`` for state variables: Disallows assignment (except initialisation), does not occupy storage slot.
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- ``immutable`` for state variables: Allows exactly one assignment at construction time and is constant afterwards. Is stored in code.
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- ``anonymous`` for events: Does not store event signature as topic.
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- ``indexed`` for event parameters: Stores the parameter as topic.
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- ``virtual`` for functions and modifiers: Allows the function's or modifier's
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behaviour to be changed in derived contracts.
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- ``override``: States that this function, modifier or public state variable changes
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the behaviour of a function or modifier in a base contract.
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Reserved Keywords
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=================
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These keywords are reserved in Solidity. They might become part of the syntax in the future:
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``after``, ``alias``, ``apply``, ``auto``, ``byte``, ``case``, ``copyof``, ``default``,
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``define``, ``final``, ``implements``, ``in``, ``inline``, ``let``, ``macro``, ``match``,
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``mutable``, ``null``, ``of``, ``partial``, ``promise``, ``reference``, ``relocatable``,
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``sealed``, ``sizeof``, ``static``, ``supports``, ``switch``, ``typedef``, ``typeof``,
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``var``.
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