wiki/content/20200928193245-embedding.md

---
id: 8f08356d-b0dc-465b-b7f5-5522b5133916
title: Golang Embedding
---

# Description

[Embedding](https://golang.org/doc/effective_go.html#embedding) is Gos
answer to subclasses. There's one caveat:

> There's an important way in which embedding differs from subclassing.
> When we embed a type, the methods of that type become methods of the
> outer type, but when they are invoked the receiver of the method is
> the inner type, not the outer one.

# Interfaces

``` go
type Reader interface {
    Read(p []byte) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

type ReadWriter interface {
    Reader
    Writer
}
```

`ReadWriter` "extends" `Reader` & `Writer` in the example above.

# Structs

``` go
type ReadWriter struct {
    *Reader  // *bufio.Reader
    *Writer  // *bufio.Writer
}

func (rw *ReadWriter) Read(p []byte) (n int, err error) {
    return rw.reader.Read(p)
}
```