WTF Solidity: 16. Overloading

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Overloading

solidity allows functions to be overloaded（overloading）.That is, functions with the same name but different input parameter types can exist at the same time, and they are regarded as different functions. Note that solidity does not allow modifier (modifier) to be overloaded.

Function Overloading

For example, we could define two functions both called saySomething(): one without any arguments and outputting "Nothing", the other taking a string argument and outputting a string.

function saySomething() public pure returns(string memory){
    return("Nothing");
}

function saySomething(string memory something) public pure returns(string memory){
    return(something);
}

After compiling, all overloading functions become different function selectors due to different parameter types. For the specific content of the function selector, please refer to WTF Solidity: 29. Function Selector.

Taking the Overloading.sol contract as an example, after compiling and deploying on Remix. After calling the overloading functions saySomething() and saySomething(string memory something) respectively, we can see different results, for the functions are regarded as different ones.

Argument Matching

When the overloading function is called, the variable type will be matched between input parameter and function parameters. An error will be reported if there are multiple matching overloading functions, The following example has two functions called f(), one have uint8 parameter and the other get uint256:

    function f(uint8 _in) public pure returns (uint8 out) {
        out = _in;
    }

    function f(uint256 _in) public pure returns (uint256 out) {
        out = _in;
    }

For 50 can be converted to uint8 as well as uint256, so it will report an error if we call f(50).

Summary

In this lecture, we introduce the basic usage of overloading function in solidity: functions with the same name but different input parameter types can exist at the same time, which are treated as different functions.