How to Correctly Initialize Nested Structures in Go Using Literals?

Nestled Structures and Field Initialization Literals

In Go, structures can embed other structures, known as nested structures. When initializing nested structures with literal member values, it's common to encounter an issue where the compiler flags an unknown field in the parent structure.

For example, consider the following code:

type A struct {
    MemberA string
}

type B struct {
    A
    MemberB string
}

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

Here, the B struct is defined to contain an anonymous field of type A. However, when trying to initialize the MemberA field of the nested A struct directly, the compiler throws an error:

unknown B field 'MemberA' in struct literal

This error occurs because during initialization, the anonymous struct is known only by its type name. The members and functions associated with the anonymous struct are not yet exported until after the instance is created.

To resolve this issue, you need to provide a valid instance of the anonymous struct (A in this case) when initializing the nested field:

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

By explicitly providing an instance of the anonymous struct, you supply the compiler with the necessary information to access the MemberA field.

The compiler error message "unknown B field 'MemberA' in struct literal" indicates that the MemberA field is not recognized within the B struct context because it belongs to the anonymous A struct.

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