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Merge pull request #1787 from ethereum/docs-gasvalue

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Document the .value() and .gas() modifiers
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chriseth 2017-03-16 15:52:10 +01:00 committed by GitHub
commit 58334cf4ac
2 changed files with 7 additions and 5 deletions
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10
docs/control-structures.rst
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@ -113,8 +113,8 @@ actual contract has not been created yet.
Functions of other contracts have to be called externally. For an external call, Functions of other contracts have to be called externally. For an external call,
all function arguments have to be copied to memory. all function arguments have to be copied to memory.
When calling functions When calling functions of other contracts, the amount of Wei sent with the call and
of other contracts, the amount of Wei sent with the call and the gas can be specified:: the gas can be specified with special options ``.value()`` and ``.gas()``, respectively::
contract InfoFeed { contract InfoFeed {
function info() payable returns (uint ret) { return 42; } function info() payable returns (uint ret) { return 42; }
@ -127,8 +127,8 @@ of other contracts, the amount of Wei sent with the call and the gas can be spec
function callFeed() { feed.info.value(10).gas(800)(); } function callFeed() { feed.info.value(10).gas(800)(); }
} }
The modifier ``payable`` has to be used for ``info``, because otherwise, The modifier ``payable`` has to be used for ``info``, because otherwise, the `.value()`
we would not be able to send Ether to it in the call ``feed.info.value(10).gas(800)()``. option would not be available.
Note that the expression ``InfoFeed(addr)`` performs an explicit type conversion stating Note that the expression ``InfoFeed(addr)`` performs an explicit type conversion stating
that "we know that the type of the contract at the given address is ``InfoFeed``" and that "we know that the type of the contract at the given address is ``InfoFeed``" and
@ -235,7 +235,7 @@ creation-dependencies are not possible.
} }
} }
As seen in the example, it is possible to forward Ether to the creation, As seen in the example, it is possible to forward Ether to the creation using the ``.value()`` option,
but it is not possible to limit the amount of gas. If the creation fails but it is not possible to limit the amount of gas. If the creation fails
(due to out-of-stack, not enough balance or other problems), an exception (due to out-of-stack, not enough balance or other problems), an exception
is thrown. is thrown.

2
docs/types.rst
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@ -123,6 +123,8 @@ In a similar way, the function ``delegatecall`` can be used: The difference is t
All three functions ``call``, ``delegatecall`` and ``callcode`` are very low-level functions and should only be used as a *last resort* as they break the type-safety of Solidity. All three functions ``call``, ``delegatecall`` and ``callcode`` are very low-level functions and should only be used as a *last resort* as they break the type-safety of Solidity.
The ``.gas()`` option is available on all three methods, while the ``.value()`` option is not supported for ``delegatecall``.
.. note:: .. note::
All contracts inherit the members of address, so it is possible to query the balance of the All contracts inherit the members of address, so it is possible to query the balance of the
current contract using ``this.balance``. current contract using ``this.balance``.