Go Interfaces Tutorial

Introduction

This lab is about interfaces in Golang. Interfaces are named collections of method signatures.

Interfaces

The problem is to implement an interface in Go, we just need to implement all the methods in the interface. Here we implement geometry on rects and circles.

• Implement an interface in Go.
• Implement all the methods in the interface.
• Use a generic measure function to work on any geometry.
• Use instances of circle and rect structs as arguments to measure.

$ go run interfaces.go
{3 4}
12
14
{5}
78.53981633974483
31.41592653589793

## To learn more about Go's interfaces, check out this
## [great blog post](https://jordanorelli.tumblr.com/post/32665860244/how-to-use-interfaces-in-go).

There is the full code below:

// _Interfaces_ are named collections of method
// signatures.

package main

import (
	"fmt"
	"math"
)

// 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 `rect`s.
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 `circle`s.
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())
}

func main() {
	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)
}

Summary

This lab is about implementing an interface in Go. We implemented the geometry interface on rects and circles and used a generic measure function to work on any geometry.