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Merge pull request #458 from ethereum/MappingOfMappingExample

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Update frequently-asked-questions.rst
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chriseth 2016-03-30 01:45:15 +02:00
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docs/frequently-asked-questions.rst
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@ -172,6 +172,23 @@ Are mappings iterable?
Mappings themselves are not iterable, but you can use a higher-level
datastructure on top of it, for example the `iterable mapping <https://github.com/ethereum/dapp-bin/blob/master/library/iterable_mapping.sol>`_.
Can I put arrays inside of a mapping? How do I make a mapping of a mapping?
===========================================================================
Mappings are already syntactically similar to arrays as they are, therefore it doesn't make much sense to store an array in them. Rather what you should do is create a mapping of a mapping.
An example of this would be::
contract c {
struct myStruct {
uint someNumber;
string someString;
}
mapping(uint => mapping(string => myStruct)) myDynamicMapping;
function storeInMapping() {
myDynamicMapping[1]["Foo"] = myStruct(2, "Bar");
}
}
Can you return an array or a string from a solidity function call?
==================================================================