package learning

import (
	"fmt"
	"math"
)

type InterfaceVertex struct {
	X, Y float64
}

type Abser interface {
	Abs() float64
}

func InterfaceLearning() {
	var a Abser
	f := MyFloat(-math.Sqrt2)
	v := InterfaceVertex{3, 4}

	a = f  // a MyFloat implemets Abser
	a = &v // a *InterfaceVertex implemets Abser

  // In following line, v is InterfaceVertex (not *InterfaceVertex)
  // and does NOT implement Abser
  // a = v
  fmt.Println(a.Abs())
}

type MyFloat float64

func (f MyFloat) Abs() float64 {
	if f < 0 {
		return float64(-f)
	}
	return float64(f)
}

func (v *InterfaceVertex) Abs() float64 {
	return math.Sqrt(v.X*v.X + v.Y*v.Y)
}