Default Values and Distinguishing Uninitialized Fields in Go

In Go, primitive types have default values. For instance, integers (int) are initialized to 0. However, when working with structs, distinguishing between a 0 value and an uninitialized field can be challenging.

For example, consider the code below:

package main

import "log"

type test struct {
    testIntOne int
    testIntTwo int
}

func main() {
    s := test{testIntOne: 0}

    log.Println(s)
}

In this code, both testIntOne and testIntTwo are zero. However, testIntOne has been explicitly set to 0, while testIntTwo has been initialized by the default value. This ambiguity can lead to confusion in determining which fields have been explicitly set.

Is it possible to distinguish between these two cases?

No, Go does not track whether a field has been set or not. Therefore, it is impossible to know if a zero value is the result of initialization or an intentional assignment.

Workarounds

• Use Pointers: Pointers have a nil zero value, so you can check if a pointer has been set by examining whether it is nil.

type test struct {
    testIntOne *int
    testIntTwo *int
}

• Create a Setter Method: You can create a method to set the value of a field and track whether it has been set.

type test struct {
    testIntOne int
    testIntTwo bool // Tracks if testIntTwo has been set
}

func (t *test) SetTestIntTwo(val int) {
    t.testIntTwo = val
    t.isSetTestIntTwo = true
}

func main() {
    s := test{}
    s.SetTestIntTwo(0)
    fmt.Println(s.isSetTestIntTwo) // Output: true
}