Hiding nil values, understanding why golang fails here

Question

I fail to understand how to correctly assure that something is not nil in this case:

package main

type shower interface {
  getWater() []shower         


        

Answer 1

Let's think of an interface as a pointer.

Say you have a pointer a and it's nil, pointing to nothing.

var a *int // nil

Then you have a pointer b and it's pointing to a.

var b **int
b = &a // not nil

See what happened? b points to a pointer that points to nothing. So even if it's a nil pointer at the end of the chain, b does point to something - it isn't nil.

If you'd peek at the process' memory, it might look like this:

address | name | value
1000000 | a    | 0
2000000 | b    | 1000000

See? a is pointing to address 0 (which means it's nil), and b is pointing to the address of a (1000000).

The same applies to interfaces (except that they look a bit different in memory).

Like a pointer, an interface pointing to a nil pointer would not be nil itself.

Here, see for yourself how this works with pointers and how it works with interfaces.