Post

Add methods to anything

Posted
By Chris Lesiw
1 min read

Go methods don’t have to be declared on structs.

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package main

import "fmt"

type chanWriter chan string

func (w chanWriter) Write(b []byte) (int, error) {
    w <- string(b)
    return len(b), nil
}

func main() {
    w := make(chanWriter)
    go func() {
        fmt.Fprintln(&w, "Hello, world!")
        close(w)
    }()
    for s := range w {
        print(s)
    }
}

// Output: Hello, world!

Playground

In fact, methods can even be declared on functions. This can be useful when you want the simplest possible thing that fulfills an interface.

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package main

import (
    "fmt"
    "log"
    "net/http"
)

type handler func(http.ResponseWriter, *http.Request)

func (f handler) ServeHTTP(w http.ResponseWriter, r *http.Request) { f(w, r) }

func main() {
    h := handler(func(w http.ResponseWriter, _ *http.Request) {
        fmt.Fprintf(w, "Hello, world!")
    })
    http.Handle("/", h)
    log.Fatal(http.ListenAndServe(":8080", nil))
}
go
golang