Listing interfaces in interfaces in Go

Question

I don't understand the following code snippet in the container/heap package.

type Interface interface {
    sort.Interface   //Is this line a method?
    Push(x interface{})
    Pop() interface{}
}

Answer 1

This is a type declaration.

The heap.Interface interface embeds the sort.Interface interface.

You can see it as a kind of inheritance/specialization : it means that the structs implementing the heap.Interface interface are defined as the ones that implement the sort.Interface methods and the Push and Pop methods.

Interface embeding is described in Effective Go : http://golang.org/doc/effective_go.html#embedding