nested struct initialization literals

struct go nested literals
Brad Peabody picture Brad Peabody · Oct 11, 2013 · Viewed 13.6k times · Source

How can I do this:

type A struct {
    MemberA string
}

type B struct {
    A
    MemberB string
}

...

b := B {
    MemberA: "test1",
    MemberB: "test2",
}
fmt.Printf("%+v\n", b)

Compiling that gives me: "unknown B field 'MemberA' in struct literal"

How can I initialize MemberA (from the "parent" struct) when I provide literal struct member values like this?

Answer

nemo picture nemo · Oct 11, 2013

While initialization the anonymous struct is only known under its type name (in your case A). The members and functions associated with the struct are only exported to the outside after the instance exists.

You have to supply a valid instance of A to initialize MemberA:

b := B {
    A: A{MemberA: "test1"},
    MemberB: "test2",
}

The compiler error

unknown B field 'MemberA' in struct literal

says exactly that: there's no MemberA as it is still in A and not in B. In fact, B will never have MemberA, it will always remain in A. Being able to access MemberA on an instance of B is only syntactic sugar.

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