When upgrading contracts can you change the logic inside functions?

Question

I am trying to wrap my head around all this and am looking for someone to help clarify.

Lets say I have the following:

contract Test {
    public c = 3;
    function A(uint a) returns(uint){
    
       uint b = a - c;
       return b;
    }
    
    function B() returns(uint){
       return b + a;
    }
    
}

Now I have found a bug in my code and function A should be this:

contract Test {
    public c = 3;
    function A(uint a) returns(uint){

       uint b = a - C();
       return b;
    }

    function B() returns(uint){
       return b + a;
    }
    
    function C() returns(uint) {
       return c * 2;
    }
}

Would this work in with upgrading proxy?

Answer 1

Yes. If you are using the proxy delegate pattern, your upgrade would work!

One important rule is to avoid overwriting your state. So, in your case, your contracts would break if you added a new variable on the line before public c = 3;.