Iterate over an interface

Question

I want to create a function that takes either a map or an array of whatever and iterates over it calling a function on each item which knows what to do with whatever types i

Answer 1

For your example to work, you would need to build an array of interface{} (or a map), in order for the right type to be detected:

// This won't work, as the .(type) would be []S
someS := []S{S{}}
DoTheThingToAllTheThings(someS)

// This will: it will go in case []interface{}:
someSI := make([]interface{}, len(someS))
for i, s := range someS {
    someSI[i] = s
}
DoTheThingToAllTheThings(someSI)

See a full example here.

But that means you would still work with interface{} in your DoTheThing function.
There is no real generic here, as I mentioned in "What would generics in Go be?".