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Document constant functions

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Alex Beregszaszi 2016-10-15 22:34:35 +01:00
parent f0f2d5a612
commit 1b3713742f
2 changed files with 24 additions and 17 deletions
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27
docs/contracts.rst
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@ -421,9 +421,9 @@ change by overriding).
.. index:: ! constant
**********
Constants
**********
************************
Constant State Variables
************************
State variables can be declared as constant (this is not yet implemented
for array and struct types and not possible for mapping types).
@ -442,6 +442,27 @@ for these variables and every occurrence is replaced by their constant value.
The value expression can only contain integer arithmetics.
******************
Constant Functions
******************
Functions can be declared constant. These functions promise not to modify the state.
::
pragma solidity ^0.4.0;
contract C {
function f(uint a, uint b) constant returns (uint) {
return a * (b + 42);
}
}
.. note::
Accessor methods are marked constant.
.. warning::
The compiler does not enforce yet that a constant method is not modifying state.
.. index:: ! fallback function, function;fallback

14
docs/frequently-asked-questions.rst
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@ -97,20 +97,6 @@ Its type is the type of the contract. Since any contract type basically inherits
``address`` type, ``this`` is always convertible to ``address`` and in this case contains
its own address.
What is the difference between a function marked ``constant`` and one that is not?
==================================================================================
``constant`` functions can perform some action and return a value, but cannot
change state (this is not yet enforced by the compiler). In other words, a
constant function cannot save or update any variables within the contract or wider
blockchain. These functions are called using ``c.someFunction(...)`` from
geth or any other web3.js environment.
"non-constant" functions (those lacking the ``constant`` specifier) must be called
with ``c.someMethod.sendTransaction({from:eth.accounts[x], gas: 1000000});``
That is, because they can change state, they have to have a gas
payment sent along to get the work done.
Get a contract to return its funds to you (not using ``selfdestruct(...)``).
============================================================================