Private embedded struct when importing a struct from another package

Question

I have a project which relies on a struct imported from another package, which I will call TheirEntity.

In the example below, I (ahem) embed TheirEntity in MyEntity, which is an extension of TheirEntity, with added functionality.

However, I don't want to export TheirEntity in the MyEntity structure, as I would rather the consumer not access TheirEntity directly.

I know that Go embedding is not the same as inheritance in classical OOP, so maybe this is not the correct approach, but is it possible to specify embedded structs as "private", even if they are imported from another package? How might one achieve the same thing in a more idiomatic fashion?

// TheirEntity contains functionality I would like to use...

type TheirEntity struct {
    name string
}

func (t TheirEntity) PrintName() {
    fmt.Println(t.name)
}

func NewTheirEntity(name string) *TheirEntity {
    return &TheirEntity{name: name}
}

// ... by embedding in MyEntity

type MyEntity struct {
    *TheirEntity // However, I don't want to expose 
                 // TheirEntity directly. How to embed this
                 // without exporting and not changing this
                 // to a named field?

    color        string
}

func (m MyEntity) PrintFavoriteColor() {
    fmt.Println(m.color)
}

func NewMyEntity(name string, color string) *MyEntity {
    return &MyEntity{
        TheirEntity: NewTheirEntity(name),
        color:       color,
    }
}

Answer 1

[I]s it possible to specify embedded structs as "private", even if they are imported from another package?

No.

How might one achieve the same thing in a more idiomatic fashion?

By not-embedding but making it a unexported named field.

Answer 2

Since the question was asked, Go saw the addition of type aliases to the language with the 1.9 release in 2017. It turns out that, through an unconventional use of type aliases, you can have your cake and eat it too!

First, declare an unexported alias for the third-party type you wish to embed in your struct:

type theirEntity = TheirEntity

Then, simply embed that alias instead of the original type:

type MyEntity struct {
    *theirEntity
    color string
}

(Playground)

Answer 3

Like this:

type MyEntity struct {
    *privateTheirEntity
}

type privateTheirEntity struct {
    *TheirEntity
}