typechecking.sol

pragma solidity ^0.4.0;

contract ISomething {
    function fooSomething() returns(uint);
}

contract BarGuy {
    // This internal function use the type system for additional safety guarantees onthe input addres. 
    function barThing (ISomething _iSomething) internal returns(uint){
        uint x = _iSomething.fooSomething();
    }
}

contract BarDad is BarGuy {
    function barbarbar(address _addr){
        uint a = barThing(_addr);  // TypeError: Invalid type for argument in function call. Invalid implicit conversion from address to contract ISomething requested.
        uint a = barThing(_addr);
    }
}