Why is "const true = false" allowed?

Question

1. What version of Go are you using (go version)? https://play.golang.org

2. What did you do?

Run a small program:

package main

import "fmt"

const true = false

func main() {
    if (true == false) {
        fmt.Println("True equals to false")
    }
    fmt.Println("Hello World")
}

https://play.golang.org/p/KwePsmQ_q9

3. What did you expect to see?

Error or warning message that I'm creating constant with already defined name, and potentially breaking whole app.

4. What did you see instead?

Running without a problem. No warnings or anything to prevent creating new constant with already defined name.

Answer 1

true and false are not reserved keywords. These are predeclared identifiers.

const (
        true  = 0 == 0 // Untyped bool.
        false = 0 != 0 // Untyped bool.
)

This means that true and false are simple two untyped boolean values. This is the reason that in your example true is equal to false.

https://golang.org/pkg/builtin/#pkg-constants