Go Interfaces Tutorial

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Introduction

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


Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL go(("`Go`")) -.-> go/ObjectOrientedProgrammingGroup(["`Object-Oriented Programming`"]) go/ObjectOrientedProgrammingGroup -.-> go/interfaces("`Interfaces`") subgraph Lab Skills go/interfaces -.-> lab-15484{{"`Go Interfaces Tutorial`"}} end

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.

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