Initialize struct with global scope where type depends on boolean

Question

I started using Golang recently and stumbled across a problem:

I have two structs, human and alien, which are both based on the creature struct. I want to initialize one of them based on the value of the isAlien boolean inside of an if-statement.

Using the human := human{} notation or the alien equivalent inside the if blocks to initialize, the instances aren't accessible from outside of the if-statement.

On the other hand, the usual solution of declaring the type and the name of the variable before the if-statement and initializing the variable inside the if-statement doesn't work, because there two are different types:

var h human //use human or alien here?
if isAlien {
  h = alien{} //Error: incompatible types
} else {
 h = human{}
}
//same when swapping human with alien at the declaration

I know that I could just declare both types before the if-statement but that solution doesn't seem elegant to me.

Is there some obvious solution that I'm missing here?

Answer 1

As you noted, the problem is clearly represented by this statement:

var h human //use human or alien here?

If you plan to use that h variable there after creating the objects, then the type of h must be one that can accept either a human or alien as a value.

The way to do this in Go is by using an ìnterface that both alien and human can fulfil.

So you should declare an interface like:

type subject interface {
    // you should list all functions that you plan to use on "h" afterwards
    // both "human" and "alien" must implement those functions 
}

Then:

var h subject

Will do the trick.