What limitations exist in the Go language to prevent an interface from being declared empty?

In the Go language, an interface can be declared empty — this is a special case of an interface, denoted as interface{}.

An empty interface can hold values of any type, as all types implement it automatically.

Therefore, there are no restrictions on declaring an empty interface in Go — it is valid and widely used.

If the question is how to make an interface non-empty, then you need to declare at least one method in it:

// Empty interface
var i interface{}

// Interface with a method
type Reader interface {
    Read(p []byte) (n int, err error)
}

Thus, an empty interface is a basic building block in Go, and there are no restrictions on its declaration.