interfaces.go

package main

import (
	"fmt"
	"math"
)

// Interfaces are named collections of method signatures.

// Here’s a basic interface for geometric shapes.
type geometry interface {
	area() float64
	perim() float64
}

// For our example we’ll implement this interface on rect and circle types.
type rect struct {
	width, height float64
}

type circle struct {
	radius float64
}

// To implement an interface in Go, we just need to implement all the methods in the interface.
// Here we implement geometry on rects.
func (r rect) area() float64 {
	return r.width * r.height
}
func (r rect) perim() float64 {
	return 2*r.width + 2*r.height
}

// The implementation for circles.
func (c circle) area() float64 {
	return math.Pi * c.radius * c.radius
}
func (c circle) perim() float64 {
	return 2 * math.Pi * c.radius
}

// If a variable has an interface type, then we can call methods that are in the named interface.
// Here’s a generic measure function taking advantage of this to work on any geometry.
func measure(g geometry) {
	fmt.Println(g)
	fmt.Println(g.area())
	fmt.Println(g.perim())
}

// Interfaces function illustrate interfaces in go.
func Interfaces() {
	r := rect{width: 3, height: 4}
	c := circle{radius: 5}

	// The circle and rect struct types both implement the geometry interface so we can use instances
	// of these structs as arguments to measure.
	measure(r)
	measure(c)
}