Solidity functions, like any other programming language,
take input parameters and return output parameters. They can also return
arbitrary number of parameters as output (this is similar to Tuples in C#
7).
Input Parameters
The input parameters are defined same as variables. A
function can take multiple number of input parameters. In our service if we
want to hire a contractor we specify the contract address as the input
parameter.
/// @notice hiring the
contractor to perform the work
/// @param _contractor
ethereum address of the contractor
function hire (address _contractor)
onlyClient {
contractor = _contractor;
}
Output Parameters
Solidity functions support multiple ways of returning
parameters. The function return type should be declared with returns keyword. In
our service if we want to return the contractor address, then we would write as
below:
/// @notice Get the
contractor assigned to the service
/// @return contractor
address
function getContractorAddress()
public constant returns (address) {
return contractor;
}
Similar to other languages we can use the keyword return to return the function
output. Solidity supports named parameters we can provide name of the return
parameter as shown below:
/// @notice Get the
contractor assigned to the service
/// @return contractor
address
function getContractorAddress()
public constant returns (address _contractor) {
_contractor = contractor;
}
In the above code we provided variable name to the return
parameter, _contractor. Assigning value to the variable will automatically
return its value.
Solidity supports returning values. It internally uses tuple
types, i.e. a list of objects of potentially different types whose size is a
constant at compile-time. Those tuples can be used to return multiple values at
the same time. The functionality is similar to tuples in C# 7. Let’s return all
the addresses in our Service Contract
/// @notice Get the
addresses of client, contractor and 0x platform
/// @return client, contractor
and platform address
function getAllAddresses() public constant returns (address, address, address) {
return (client, contractor, platform);
}
