What's the meaning of interface{}?

Question

I\'m new to interfaces and trying to do SOAP request by github

I don\'t understand the meaning of

Msg interface{}

in this code:

Answer 1

There are already good answers here. Let me add my own too for others who want to understand it intuitively:

---

Interface

Here's an interface with one method:

type Runner interface {
    Run()
}

So any type that has a Run() method satisfies the Runner interface:

type Program struct {
    /* fields */
}

func (p Program) Run() {
    /* running */
}

func (p Program) Stop() {
    /* stopping */
}

• Although the Program type has also a Stop method, it still satisfies the Runner interface because all that is needed is to have all of the methods of an interface to satisfy it.

• So, it has a Run method and it satisfies the Runner interface.

---

Empty Interface

Here's a named empty interface without any methods:

type Empty interface {
    /* it has no methods */
}

So any type satisfies this interface. Because, no method is needed to satisfy this interface. For example:

// Because, Empty interface has no methods, following types satisfy the Empty interface
var a Empty

a = 5
a = 6.5
a = "hello"

But, does the Program type above satisfy it? Yes:

a = Program{} // ok

interface{} is equal to the Empty interface above.

var b interface{}

// true: a == b

b = a
b = 9
b = "bye"

As you see, there's nothing mysterious about it but it's very easy to abuse. Stay away from it as much as you can.

---

https://play.golang.org/p/A-vwTddWJ7G