检查Go中是否设置了布尔值

Question

Is it possible to differentiate between false and an unset boolean value in go?

For instance, if I had this code

type Test struct {
    Set bool
    Unset bool
}

test := Test{ Set: false }

Is there any difference between test.Set and test.Unset and if so how can I tell them apart?

Answer 1

No, a bool has two possibilities: true or false. The default value of an uninitialized bool is false. If you want a third state, you can use *bool instead, and the default value will be nil.

type Test struct {
    Set *bool
    Unset *bool
}

f := false
test := Test{ Set: &f }

fmt.Println(*test.Set)  // false
fmt.Println(test.Unset) // nil

The cost for this is that it is a bit uglier to set values to literals, and you have to be a bit more careful to dereference (and check nil) when you are using the values.

Playground link