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.

2 Answers 2


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.


I've found a hacky solution that uses inline assembly, but would love a more "native" solution if there is one.

modifier restrictTargetType(uint contractType) {
  if (contractTypes[_getFirstArg(msg.data)] != contractType) { throw; }

function _getFirstArg(bytes calldata) returns(address result) {
  assembly {
    calldatacopy(mload(0x40), 4, 32)
    result := mload(mload(0x40))

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