How does the delegatecall method work to call to another contract's method?

Question

I'm trying to figure out how to use the delegatecall method on a contract address in a contract to call a function in a separate contract.

I know Libraries are the higher level interface to use but I want to understand the lower level actions and behaviors.

If someone could provide some good examples of a contract using delegatecall to another contract's functions, that would be greatly appreciated.

Answer 1

Here is a snippet of D using delegatecall on E from Difference between CALL, CALLCODE and DELEGATECALL

contract D {
  uint public n;
  address public sender;

  function delegatecallSetN(address _e, uint _n) {
    _e.delegatecall(bytes4(keccak256("setN(uint256)")), _n); // D's storage is set, E is not modified 
  }
}

contract E {
  uint public n;
  address public sender;
  function setN(uint _n) {
    n = _n;
    sender = msg.sender;
  }
}

When an address C invokes delegatecallSetN, D's sender will be set to C (E is not modified). Whatever msg.value is part of the invocation, will also be the value of msg.value inside setN.

You can quickly test above in Solidity Browser.

For libraries see the Solidity docs.