Interfaces in golang

Tue, 11 Jan 2022 08:48:23 +0000

TL;DR:

An interface just defines a collection of methods. When you create an instance, it’s just a wrapper around a concrete type. In addition to the concrete type, the interface contains an extra array of function pointers. These function pointers correspond to each method in the interface that the concrete type implements

First, a detour

Let’s define a custom type, and some methods that go with it:

package main

import "fmt"

type ComputerProgrammer string

func (c ComputerProgrammer) Greet(name string) string {
	return string(c) + ": hello, " + name
}

func (c ComputerProgrammer) Walk(distance int) int {
	return len(c) + distance
}

func main() {
	a := ComputerProgrammer("golang")
	fmt.Println(a.Greet("world"), a.Walk(5))
}

When go compiles this code, it generates a function similar to this:

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Interfaces in golang

TL;DR:

First, a detour