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| -rw-r--r-- | docs/contracts.rst | 101 |
1 files changed, 94 insertions, 7 deletions
diff --git a/docs/contracts.rst b/docs/contracts.rst index 2b0956bb..ca4e79c0 100644 --- a/docs/contracts.rst +++ b/docs/contracts.rst @@ -426,12 +426,20 @@ value types and strings. bytes32 constant myHash = keccak256("abc"); } +.. index:: ! functions + +.. _functions: + +********* +Functions +********* + +.. index:: ! view function, function;view .. _view-functions: -************** View Functions -************** +============== Functions can be declared ``view`` in which case they promise not to modify the state. @@ -465,11 +473,12 @@ The following statements are considered modifying the state: .. warning:: The compiler does not enforce yet that a ``view`` method is not modifying state. +.. index:: ! pure function, function;pure + .. _pure-functions: -************** Pure Functions -************** +============== Functions can be declared ``pure`` in which case they promise not to read from or modify the state. @@ -498,9 +507,8 @@ In addition to the list of state modifying statements explained above, the follo .. _fallback-function: -***************** Fallback Function -***************** +================= A contract can have exactly one unnamed function. This function cannot have arguments and cannot return anything. @@ -577,6 +585,85 @@ Please ensure you test your fallback function thoroughly to ensure the execution } } +.. index:: ! overload + +.. _overload-function: + +Function Overloading +==================== + +A Contract can have multiple functions of the same name but with different arguments. +This also applies to inherited functions. The following example shows overloading of the +``f`` function in the scope of contract ``A``. + +:: + + pragma solidity ^0.4.16; + + contract A { + function f(uint _in) public pure returns (uint out) { + out = 1; + } + + function f(uint _in, bytes32 _key) public pure returns (uint out) { + out = 2; + } + } + +Overloaded functions are also present in the external interface. It is an error if two +externally visible functions differ by their Solidity types but not by their external types. + +:: + + // This will not compile + pragma solidity ^0.4.16; + + contract A { + function f(B _in) public pure returns (B out) { + out = _in; + } + + function f(address _in) public pure returns (address out) { + out = _in; + } + } + + contract B { + } + + +Both ``f`` function overloads above end up accepting the address type for the ABI although +they are considered different inside Solidity. + +Overload resolution and Argument matching +----------------------------------------- + +Overloaded functions are selected by matching the function declarations in the current scope +to the arguments supplied in the function call. Functions are selected as overload candidates +if all arguments can be implicitly converted to the expected types. If there is not exactly one +candidate, resolution fails. + +.. note:: + Return parameters are not taken into account for overload resolution. + +:: + + pragma solidity ^0.4.16; + + contract A { + function f(uint8 _in) public pure returns (uint8 out) { + out = _in; + } + + function f(uint256 _in) public pure returns (uint256 out) { + out = _in; + } + } + +Calling ``f(50)`` would create a type error since ``250`` can be implicitly converted both to ``uint8`` +and ``uint256`` types. On another hand ``f(256)`` would resolve to ``f(uint256)`` overload as ``256`` cannot be implicitly +converted to ``uint8``. + .. index:: ! event .. _events: @@ -854,7 +941,7 @@ derived override, but this function will bypass } If ``Base1`` calls a function of ``super``, it does not simply -call this function on one of its base contracts. Rather, it +call this function on one of its base contracts. Rather, it calls this function on the next base contract in the final inheritance graph, so it will call ``Base2.kill()`` (note that the final inheritance sequence is -- starting with the most |