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Split Function modifiers doc into smaller file
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Chris Ward
chriseth
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commit
c9b2e5da8f
@ -16,117 +16,7 @@ inaccessible.
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.. include:: contracts/visibility-and-getters.rst
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.. index:: ! function;modifier
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.. _modifiers:
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******************
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Function Modifiers
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******************
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Modifiers can be used to easily change the behaviour of functions. For example,
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they can automatically check a condition prior to executing the function. Modifiers are
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inheritable properties of contracts and may be overridden by derived contracts.
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::
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pragma solidity ^0.5.0;
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contract owned {
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constructor() public { owner = msg.sender; }
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address payable owner;
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// This contract only defines a modifier but does not use
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// it: it will be used in derived contracts.
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// The function body is inserted where the special symbol
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// `_;` in the definition of a modifier appears.
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// This means that if the owner calls this function, the
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// function is executed and otherwise, an exception is
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// thrown.
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modifier onlyOwner {
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require(
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msg.sender == owner,
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"Only owner can call this function."
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);
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_;
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}
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}
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contract mortal is owned {
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// This contract inherits the `onlyOwner` modifier from
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// `owned` and applies it to the `close` function, which
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// causes that calls to `close` only have an effect if
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// they are made by the stored owner.
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function close() public onlyOwner {
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selfdestruct(owner);
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}
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}
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contract priced {
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// Modifiers can receive arguments:
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modifier costs(uint price) {
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if (msg.value >= price) {
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_;
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}
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}
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}
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contract Register is priced, owned {
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mapping (address => bool) registeredAddresses;
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uint price;
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constructor(uint initialPrice) public { price = initialPrice; }
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// It is important to also provide the
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// `payable` keyword here, otherwise the function will
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// automatically reject all Ether sent to it.
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function register() public payable costs(price) {
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registeredAddresses[msg.sender] = true;
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}
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function changePrice(uint _price) public onlyOwner {
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price = _price;
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}
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}
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contract Mutex {
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bool locked;
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modifier noReentrancy() {
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require(
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!locked,
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"Reentrant call."
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);
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locked = true;
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_;
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locked = false;
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}
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/// This function is protected by a mutex, which means that
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/// reentrant calls from within `msg.sender.call` cannot call `f` again.
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/// The `return 7` statement assigns 7 to the return value but still
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/// executes the statement `locked = false` in the modifier.
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function f() public noReentrancy returns (uint) {
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(bool success,) = msg.sender.call("");
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require(success);
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return 7;
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}
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}
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Multiple modifiers are applied to a function by specifying them in a
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whitespace-separated list and are evaluated in the order presented.
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.. warning::
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In an earlier version of Solidity, ``return`` statements in functions
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having modifiers behaved differently.
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Explicit returns from a modifier or function body only leave the current
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modifier or function body. Return variables are assigned and
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control flow continues after the "_" in the preceding modifier.
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Arbitrary expressions are allowed for modifier arguments and in this context,
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all symbols visible from the function are visible in the modifier. Symbols
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introduced in the modifier are not visible in the function (as they might
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change by overriding).
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.. include:: contracts/function-modifiers.rst
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.. include:: contracts/constant-state-variables.rst
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111
docs/contracts/function-modifiers.rst
Normal file
111
docs/contracts/function-modifiers.rst
Normal file
@ -0,0 +1,111 @@
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.. index:: ! function;modifier
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.. _modifiers:
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******************
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Function Modifiers
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******************
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Modifiers can be used to easily change the behaviour of functions. For example,
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they can automatically check a condition prior to executing the function. Modifiers are
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inheritable properties of contracts and may be overridden by derived contracts.
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::
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pragma solidity ^0.5.0;
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contract owned {
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constructor() public { owner = msg.sender; }
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address payable owner;
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// This contract only defines a modifier but does not use
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// it: it will be used in derived contracts.
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// The function body is inserted where the special symbol
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// `_;` in the definition of a modifier appears.
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// This means that if the owner calls this function, the
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// function is executed and otherwise, an exception is
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// thrown.
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modifier onlyOwner {
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require(
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msg.sender == owner,
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"Only owner can call this function."
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);
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_;
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}
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}
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contract mortal is owned {
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// This contract inherits the `onlyOwner` modifier from
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// `owned` and applies it to the `close` function, which
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// causes that calls to `close` only have an effect if
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// they are made by the stored owner.
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function close() public onlyOwner {
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selfdestruct(owner);
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}
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}
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contract priced {
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// Modifiers can receive arguments:
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modifier costs(uint price) {
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if (msg.value >= price) {
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_;
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}
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}
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}
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contract Register is priced, owned {
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mapping (address => bool) registeredAddresses;
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uint price;
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constructor(uint initialPrice) public { price = initialPrice; }
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// It is important to also provide the
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// `payable` keyword here, otherwise the function will
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// automatically reject all Ether sent to it.
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function register() public payable costs(price) {
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registeredAddresses[msg.sender] = true;
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}
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function changePrice(uint _price) public onlyOwner {
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price = _price;
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}
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}
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contract Mutex {
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bool locked;
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modifier noReentrancy() {
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require(
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!locked,
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"Reentrant call."
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);
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locked = true;
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_;
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locked = false;
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}
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/// This function is protected by a mutex, which means that
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/// reentrant calls from within `msg.sender.call` cannot call `f` again.
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/// The `return 7` statement assigns 7 to the return value but still
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/// executes the statement `locked = false` in the modifier.
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function f() public noReentrancy returns (uint) {
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(bool success,) = msg.sender.call("");
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require(success);
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return 7;
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}
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}
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Multiple modifiers are applied to a function by specifying them in a
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whitespace-separated list and are evaluated in the order presented.
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.. warning::
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In an earlier version of Solidity, ``return`` statements in functions
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having modifiers behaved differently.
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Explicit returns from a modifier or function body only leave the current
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modifier or function body. Return variables are assigned and
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control flow continues after the "_" in the preceding modifier.
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Arbitrary expressions are allowed for modifier arguments and in this context,
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all symbols visible from the function are visible in the modifier. Symbols
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introduced in the modifier are not visible in the function (as they might
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change by overriding).
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