Understanding the Adapter Pattern in Go

Adapter Pattern (Adapter)

Definition

Convert the interface of a class into another interface that clients expect, allowing classes that are otherwise incompatible to work together.

Understanding

Different mobile devices use various charging connectors, yet all power sources connect via a USB interface. This illustrates the need for an adapter.

Code Example

package main

import (
    "fmt"
)

type USB interface {
    Work()
}

// External function that expects a USB interface
func Charge(usb USB) {
    usb.Work()
}

// TypeC does not implement USB, cannot be charged directly
type TypeC struct{}

func (t TypeC) IPhone() {
    fmt.Println("Charge IPhone")
}

// AdapterTypeC embeds TypeC and implements USB
type AdapterTypeC struct {
    TypeC // composition
}

func (t AdapterTypeC) Work() {
    t.IPhone()
}

// Alternative adapter using a member variable
type AdapterTypeC1 struct {
    tc TypeC
}

func (t AdapterTypeC1) Work() {
    t.tc.IPhone()
}

// Micro implements USB and can charge Android devices
type Micro struct{}

func (t Micro) Work() {
    fmt.Println("Charge Android")
}

func main() {
    Charge(Micro{})
    Charge(AdapterTypeC{})
    Charge(AdapterTypeC1{tc: TypeC{}})
    // Charge(TypeC{}) // only structs that implement USB can be charged
}

Charge can only supply power to types that implement the USB interface; structs that do not must be wrapped with an adapter that provides the required interface.

Source code repository: https://github.com/gofish2020/gopattern/tree/main/structure/adapter