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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/contracts.rst | 112 | ||||
| -rw-r--r-- | docs/contracts/function-modifiers.rst | 111 |
2 files changed, 112 insertions, 111 deletions
diff --git a/docs/contracts.rst b/docs/contracts.rst index 2a713ec3..859cd9e9 100644 --- a/docs/contracts.rst +++ b/docs/contracts.rst @@ -16,117 +16,7 @@ inaccessible. .. include:: contracts/visibility-and-getters.rst -.. index:: ! function;modifier - -.. _modifiers: - -****************** -Function Modifiers -****************** - -Modifiers can be used to easily change the behaviour of functions. For example, -they can automatically check a condition prior to executing the function. Modifiers are -inheritable properties of contracts and may be overridden by derived contracts. - -:: - - pragma solidity ^0.5.0; - - contract owned { - constructor() public { owner = msg.sender; } - address payable owner; - - // This contract only defines a modifier but does not use - // it: it will be used in derived contracts. - // The function body is inserted where the special symbol - // `_;` in the definition of a modifier appears. - // This means that if the owner calls this function, the - // function is executed and otherwise, an exception is - // thrown. - modifier onlyOwner { - require( - msg.sender == owner, - "Only owner can call this function." - ); - _; - } - } - - contract mortal is owned { - // This contract inherits the `onlyOwner` modifier from - // `owned` and applies it to the `close` function, which - // causes that calls to `close` only have an effect if - // they are made by the stored owner. - function close() public onlyOwner { - selfdestruct(owner); - } - } - - contract priced { - // Modifiers can receive arguments: - modifier costs(uint price) { - if (msg.value >= price) { - _; - } - } - } - - contract Register is priced, owned { - mapping (address => bool) registeredAddresses; - uint price; - - constructor(uint initialPrice) public { price = initialPrice; } - - // It is important to also provide the - // `payable` keyword here, otherwise the function will - // automatically reject all Ether sent to it. - function register() public payable costs(price) { - registeredAddresses[msg.sender] = true; - } - - function changePrice(uint _price) public onlyOwner { - price = _price; - } - } - - contract Mutex { - bool locked; - modifier noReentrancy() { - require( - !locked, - "Reentrant call." - ); - locked = true; - _; - locked = false; - } - - /// This function is protected by a mutex, which means that - /// reentrant calls from within `msg.sender.call` cannot call `f` again. - /// The `return 7` statement assigns 7 to the return value but still - /// executes the statement `locked = false` in the modifier. - function f() public noReentrancy returns (uint) { - (bool success,) = msg.sender.call(""); - require(success); - return 7; - } - } - -Multiple modifiers are applied to a function by specifying them in a -whitespace-separated list and are evaluated in the order presented. - -.. warning:: - In an earlier version of Solidity, ``return`` statements in functions - having modifiers behaved differently. - -Explicit returns from a modifier or function body only leave the current -modifier or function body. Return variables are assigned and -control flow continues after the "_" in the preceding modifier. - -Arbitrary expressions are allowed for modifier arguments and in this context, -all symbols visible from the function are visible in the modifier. Symbols -introduced in the modifier are not visible in the function (as they might -change by overriding). +.. include:: contracts/function-modifiers.rst .. include:: contracts/constant-state-variables.rst diff --git a/docs/contracts/function-modifiers.rst b/docs/contracts/function-modifiers.rst new file mode 100644 index 00000000..376cd9fa --- /dev/null +++ b/docs/contracts/function-modifiers.rst @@ -0,0 +1,111 @@ +.. index:: ! function;modifier + +.. _modifiers: + +****************** +Function Modifiers +****************** + +Modifiers can be used to easily change the behaviour of functions. For example, +they can automatically check a condition prior to executing the function. Modifiers are +inheritable properties of contracts and may be overridden by derived contracts. + +:: + + pragma solidity ^0.5.0; + + contract owned { + constructor() public { owner = msg.sender; } + address payable owner; + + // This contract only defines a modifier but does not use + // it: it will be used in derived contracts. + // The function body is inserted where the special symbol + // `_;` in the definition of a modifier appears. + // This means that if the owner calls this function, the + // function is executed and otherwise, an exception is + // thrown. + modifier onlyOwner { + require( + msg.sender == owner, + "Only owner can call this function." + ); + _; + } + } + + contract mortal is owned { + // This contract inherits the `onlyOwner` modifier from + // `owned` and applies it to the `close` function, which + // causes that calls to `close` only have an effect if + // they are made by the stored owner. + function close() public onlyOwner { + selfdestruct(owner); + } + } + + contract priced { + // Modifiers can receive arguments: + modifier costs(uint price) { + if (msg.value >= price) { + _; + } + } + } + + contract Register is priced, owned { + mapping (address => bool) registeredAddresses; + uint price; + + constructor(uint initialPrice) public { price = initialPrice; } + + // It is important to also provide the + // `payable` keyword here, otherwise the function will + // automatically reject all Ether sent to it. + function register() public payable costs(price) { + registeredAddresses[msg.sender] = true; + } + + function changePrice(uint _price) public onlyOwner { + price = _price; + } + } + + contract Mutex { + bool locked; + modifier noReentrancy() { + require( + !locked, + "Reentrant call." + ); + locked = true; + _; + locked = false; + } + + /// This function is protected by a mutex, which means that + /// reentrant calls from within `msg.sender.call` cannot call `f` again. + /// The `return 7` statement assigns 7 to the return value but still + /// executes the statement `locked = false` in the modifier. + function f() public noReentrancy returns (uint) { + (bool success,) = msg.sender.call(""); + require(success); + return 7; + } + } + +Multiple modifiers are applied to a function by specifying them in a +whitespace-separated list and are evaluated in the order presented. + +.. warning:: + In an earlier version of Solidity, ``return`` statements in functions + having modifiers behaved differently. + +Explicit returns from a modifier or function body only leave the current +modifier or function body. Return variables are assigned and +control flow continues after the "_" in the preceding modifier. + +Arbitrary expressions are allowed for modifier arguments and in this context, +all symbols visible from the function are visible in the modifier. Symbols +introduced in the modifier are not visible in the function (as they might +change by overriding). |