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Merge pull request #3218 from elenadimitrova/documentation/2176-overload-resolution
Document function overloading
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commit
a0e67dec46
@ -426,12 +426,20 @@ value types and strings.
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bytes32 constant myHash = keccak256("abc");
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}
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.. index:: ! functions
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.. _functions:
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*********
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Functions
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*********
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.. index:: ! view function, function;view
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.. _view-functions:
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**************
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View Functions
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**************
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==============
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Functions can be declared ``view`` in which case they promise not to modify the state.
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@ -465,11 +473,12 @@ The following statements are considered modifying the state:
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.. warning::
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The compiler does not enforce yet that a ``view`` method is not modifying state.
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.. index:: ! pure function, function;pure
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.. _pure-functions:
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**************
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Pure Functions
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**************
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==============
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Functions can be declared ``pure`` in which case they promise not to read from or modify the state.
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@ -498,9 +507,8 @@ In addition to the list of state modifying statements explained above, the follo
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.. _fallback-function:
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*****************
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Fallback Function
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*****************
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=================
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A contract can have exactly one unnamed function. This function cannot have
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arguments and cannot return anything.
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@ -577,6 +585,85 @@ Please ensure you test your fallback function thoroughly to ensure the execution
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}
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}
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.. index:: ! overload
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.. _overload-function:
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Function Overloading
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====================
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A Contract can have multiple functions of the same name but with different arguments.
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This also applies to inherited functions. The following example shows overloading of the
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``f`` function in the scope of contract ``A``.
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::
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pragma solidity ^0.4.16;
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contract A {
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function f(uint _in) public pure returns (uint out) {
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out = 1;
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}
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function f(uint _in, bytes32 _key) public pure returns (uint out) {
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out = 2;
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}
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}
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Overloaded functions are also present in the external interface. It is an error if two
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externally visible functions differ by their Solidity types but not by their external types.
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::
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// This will not compile
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pragma solidity ^0.4.16;
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contract A {
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function f(B _in) public pure returns (B out) {
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out = _in;
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}
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function f(address _in) public pure returns (address out) {
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out = _in;
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}
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}
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contract B {
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}
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Both ``f`` function overloads above end up accepting the address type for the ABI although
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they are considered different inside Solidity.
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Overload resolution and Argument matching
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-----------------------------------------
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Overloaded functions are selected by matching the function declarations in the current scope
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to the arguments supplied in the function call. Functions are selected as overload candidates
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if all arguments can be implicitly converted to the expected types. If there is not exactly one
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candidate, resolution fails.
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.. note::
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Return parameters are not taken into account for overload resolution.
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::
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pragma solidity ^0.4.16;
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contract A {
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function f(uint8 _in) public pure returns (uint8 out) {
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out = _in;
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}
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function f(uint256 _in) public pure returns (uint256 out) {
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out = _in;
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}
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}
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Calling ``f(50)`` would create a type error since ``250`` can be implicitly converted both to ``uint8``
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and ``uint256`` types. On another hand ``f(256)`` would resolve to ``f(uint256)`` overload as ``256`` cannot be implicitly
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converted to ``uint8``.
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.. index:: ! event
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.. _events:
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@ -854,7 +941,7 @@ derived override, but this function will bypass
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}
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If ``Base1`` calls a function of ``super``, it does not simply
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call this function on one of its base contracts. Rather, it
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call this function on one of its base contracts. Rather, it
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calls this function on the next base contract in the final
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inheritance graph, so it will call ``Base2.kill()`` (note that
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the final inheritance sequence is -- starting with the most
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