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Go Struct Embedding

In Go, embedding is the way we achieve composition. It allows one struct to include another, giving it access to its fields and methods directly.

Basic example

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package main

import "fmt"

type base struct {
    num int
}

func (b base) describe() string {
    return fmt.Sprintf("base with num=%v", b.num)
}

type container struct {
    base // This is an embedded struct
    str  string
}

func main() {
    co := container{
        base: base{num: 1},
        str:  "some name",
    }

    // We can access fields of 'base' directly on 'co'
    fmt.Println("co.num:", co.num) // 1

    // We can also call methods of 'base' directly on 'co'
    fmt.Println("describe:", co.describe())
}

Why use Embedding?

  • Code Reuse: Instead of copying fields or methods, you can group them into a base struct and embed it.
  • Polymorphism through Interfaces: If base implements an interface, container will also implement it automatically because it "inherits" the methods.

Important Notes

  • Shadowing: If both structs have a field with the same name, the outer struct's field "shadows" the inner one. You can still access the inner one using the full path (e.g., co.base.num).
  • Not Inheritance: Even though it looks like inheritance, Go uses composition. The base struct doesn't know about the container struct.