An interface named "Number" accepts numeric types such as "Int", "Float" and so on.

number.go

package main

import "fmt"

type Number interface {
	Add(x Number) Number
	Sub(x Number) Number
}

type Int int

func (this Int) Add(x Number) Number {
	switch number := x.(type) {
	case Int:
		return this + number
	case Float:
		return Float(this) + number
	default:
		// undefined
	}
	return nil
}

func (this Int) Sub(x Number) Number {
	switch number := x.(type) {
	case Int:
		return this - number
	case Float:
		return Float(this) - number
	default:
		// undefined
	}
	return nil
}

type Float float64

func (this Float) Add(x Number) Number {
	switch number := x.(type) {
	case Int:
		return this + Float(number)
	case Float:
		return this + number
	default:
		// undefined
	}
	return nil
}

func (this Float) Sub(x Number) Number {
	switch number := x.(type) {
	case Int:
		return this - Float(number)
	case Float:
		return this - number
	default:
		// undefined
	}
	return nil
}

func main() {
	x := Int(10)
	y := Float(3.4)

	fmt.Printf("x = %v\n", x)
	fmt.Printf("y = %v\n\n", y)

	fmt.Printf("x + y = %v\n", x.Add(y))
	fmt.Printf("y + x = %v\n\n", y.Add(x))

	fmt.Printf("x - y = %v\n", x.Sub(y))
	fmt.Printf("y - x = %v\n\n", y.Sub(x))
}