Function declaration syntax: things in parenthesis before function name

Question

I\'m sorry I couldn\'t be more specific in the question title, but I was reading some Go code and I encountered function declarations of this form:

func (h handle         


        

Answer 1

This is called the 'receiver'. In the first case (h handler) it is a value type, in the second (s *GracefulServer) it is a pointer. The way this works in Go may vary a bit from some other languages. The receiving type however, works more or less like a class in most object-oriented programming. It is the thing you call the method from, much like if I put some method A in side some class Person then I would need an instance of type Person in order to call A (assuming it's an instance method and not static!).

One gotcha here is that the receiver gets pushed onto the call stack like other arguments so if the receiver is a value type, like in the case of handler then you will be working on a copy of the thing you called the method from meaning something like h.Name = "Evan" would not persist after you return to the calling scope. For this reason anything that expects to change the state of the receiver, needs to use a pointer or return the modified value (gives more of an immutable type paradigm if you're looking for that).

Here's the relevant section from the spec; https://golang.org/ref/spec#Method_sets