4

Can you provide an example of when and why you would want to define and use a function type, as a opposed to simply calling a function?

I understand how from here: https://ethereum.stackexchange.com/a/32464/44907

I just don't understand why.

2

The answer is why not?


IMHO it is not a feature that is really needed for smart contract, but it doesn't hurt to have it available.

For example it is possible to implement a kind of dispatch. (If you look at magic implementation it doesn't have an if).

pragma solidity ^0.4.25;

contract Foo {
    mapping (address => function (uint, uint) internal pure returns (uint)) k;

    event New(uint val);

    function gold(uint a, uint b) internal pure returns (uint) {
        return a + b * 10;
    }

    function silver(uint a, uint b) internal pure returns (uint) {
        return a + b * 5;
    }

    function eval(
        function (uint, uint) internal pure returns (uint) f,
        uint a,
        uint b) internal pure returns (uint)
    {
        return f(a, b);
    }

    function register() public payable {
        k[msg.sender] = msg.value > 31415 ? gold : silver;
    }

    function magic(uint a, uint b) public {
        uint val = eval(k[msg.sender], a, b);
        emit New(val);
    }
}
  • Awesome example! You could simplify this by just doing k[msg.sender](a, b) but being able to create a mapping that includes a function feels very powerful. :thumbsup: – valem Nov 21 '18 at 23:58

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