Struct Embedding

Go supports embedding of structs and interfaces to express a more seamless composition of types. This is not to be confused with //go:embed which is a go directive introduced in Go version 1.16+ to embed files and folders into the application binary.

package main

import "fmt"

type base struct {
    num int
}

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

// A container embeds a base. An embedding looks like a field without a name.
type container struct {
    base
    str string
}

func main() {

    // When creating structs with literals, we have to initialize
    // the embedding explicitly; here the embedded type serves as the field name.
    co := container{
        base: base{
            num: 1,
        },
        str: "some name",
    }

    // We can access the base’s fields directly on co, e.g. co.num.
    fmt.Printf("co={num: %v, str: %v}\n", co.num, co.str)

    // Alternatively, we can spell out the full path using the embedded type name.
    fmt.Println("also num:", co.base.num)

    // Since container embeds base, the methods of base also
    // become methods of a container.
    // Here we invoke a method that was embedded from base directly on co.
    fmt.Println("describe:", co.describe())

    type describer interface {
        describe() string
    }

    // Embedding structs with methods may be used to
    // bestow interface implementations onto other structs.
    // Here we see that a container now implements
    // the describer interface because it embeds base.
    var d describer = co
    fmt.Println("describer:", d.describe())
}

$ go run struct-embedding.go
co={num: 1, str: some name}
also num: 1
describe: base with num=1
describer: base with num=1