Struct Conversion in Go

Consider the following two structs:

type A struct {
    a int
    b string
}

type B struct {
    A
    c string
}

Suppose you have a variable of type A and want to convert it to type B. Is this possible in Go, or do you need to manually copy fields or create an explicit conversion method?

Method 1: Embedded Struct Assignment

As you mentioned in your question, embedding can be utilized for this purpose. By embedding A in B, you can convert a variable of type A to type B simply by assigning it to the embedded field. For example:

func main() {
    structA := A{a: 42, b: "foo"}
    structB := B{A: structA} // Embed structA into structB
}

This approach creates a new instance of B that contains the data from A in its embedded field.

Method 2: Manual Field Copying

Alternatively, you can manually copy the fields from A to B as follows:

func main() {
    structA := A{a: 42, b: "foo"}
    structB := B{
        A: structA, // Copy fields from structA
        c: "bar",
    }
}

This method involves creating a new instance of B and manually assigning the fields from A.

Method 3: Explicit Conversion Method

Another option is to create an explicit conversion method that converts A to B. This could be useful if you have a complex conversion logic. However, this approach is not necessary in this case, as the above methods provide a straightforward way to achieve the desired conversion.