Go🔧Core Languagebeginner

Interfaces

Go · Core Language · Run with go run

Explanation

Interfaces in Go are satisfied implicitly — a type implements an interface simply by having the required methods, with no `implements` keyword. This enables loose coupling: packages define small interfaces, and any type that happens to match can be used. The most famous Go interface is `io.Reader` with its single `Read([]byte) (int, error)` method.

Real-World Scenario

A logging library accepts an `io.Writer` interface. You can pass `os.Stdout`, a `bytes.Buffer`, a file, a network connection, or your own custom writer — all without modifying the logging library.

Quick Snippet

snippet.go

type Stringer interface {
    String() string
}

type Temperature struct {
    Celsius float64
}

// Temperature implicitly satisfies Stringer
func (t Temperature) String() string {
    return fmt.Sprintf("%.1f°C", t.Celsius)
}

func Print(s Stringer) {
    fmt.Println(s.String())
}

Print(Temperature{36.6}) // 36.6°C

Full Example

View on GitHub

interfaces.go

// Compile: go run interfaces.go
// Output:
//   36.6°C
//   -273.1°C
package main

import "fmt"

type Stringer interface {
	String() string
}

type Temperature struct {
	Celsius float64
}

func (t Temperature) String() string {
	return fmt.Sprintf("%.1f°C", t.Celsius)
}

func Print(s Stringer) {
	fmt.Println(s.String())
}

func main() {
	Print(Temperature{36.6})
	Print(Temperature{-273.15})
}

Run command

bash

go run interfaces.go

Structs

Pointers