GoLang Struct Initializer 的执行顺序

Question

Was wondering if execution order for struct initialization is guaranteed in GoLang.

Does the following code always produce

obj.a == 1 and obj.b == 2 or is it unspecified behavior?

num := 0

nextNumber := func() int {
    num += 1
    return num
}

type TwoNumbers struct {
    a int
    b int
}

obj := TwoNumbers{
    a: nextNumber(),
    b: nextNumber(),
}

Answer 1

The evaluation order is specified.

The fields are assigned in a composite literal expression. The specification says this about expressions in general:

... when evaluating the operands of an expression, assignment, or return statement, all function calls, method calls, and communication operations are evaluated in lexical left-to-right order.