[Ethereum] Can Solidity function modifiers access function arguments

modifierssolidity

I would like to have a modifier that looks like this:

modifier restrictTargetType(uint contractType) {
    if (contractTypes[target] != contractType) { throw; }
    _
}

Where target is an address passed as a function argument. Simply naming the function argument target isn't sufficient, and gives me an Error: Undeclared identifier.

Best Answer

At the point where you use the modifier, the function arguments are already in scope. This means something like the following is possible:

contract C {
  modifier restrictTargetType(address target, uint contractType) {
    require(contractTypes[target] == contractType);
    _;
  }
  function f(address target, uint contractType) restrictTargetType(target, contractType) {
    ....
  }
}

There is no generic way to provide access to the function arguments, though.

Related Solutions

Solidity Update – Why call() Function Stopped Working in Version 0.5.0

Make sure contractAddress is of type address payable. And yes, you'll need to provide an argument. E.g.:

address payable contractAddress = ...;
contractAddress.call.value(1 ether).gas(53000)("");

Solidity Modifiers – Implementing Modifiers in a Library

Library may define and use modifiers, but it cannot export them. Modifiers are compile-time feature, kind of macros. Modifier code is substituted by compiler to every method that uses this modifier. For complex modifiers this may be a problem, but you may always move modifier's logic into a function (library function, probably), and then refer to this function from within modifier. You may also implement common modifiers in interface to share them among several contracts:

library Foo {
    modifier nonZero (uint x) {
        require (x != 0);
        _;
    }

    function isPrime (uint x) public nonZero (x) returns (bool) {
        // Complicated logic here
    }
}

interface Bar {
    modifier onlyPrime (uint x) {
        require (Foo.isPrime (x));
        _;
    }
}

contract Zoo is Bar {
    function fooBar (uint x) public onlyPrime (x) {
        // Here we know that x is prime!
    }
}

Best Answer

Related Solutions

Solidity Update – Why call() Function Stopped Working in Version 0.5.0

Solidity Modifiers – Implementing Modifiers in a Library

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