为什么我可以在go中重新声明一个const？

For exmaple

package main

import "fmt"

const s string = "constant"

func main() {
    const s = 0
    fmt.Println(s)
}

actually prints

0 

Yet I declared it as "constant" before main.

I thought you were unable to change a constant. If this is not the case, why not use other types?

It's a new constant in the scope of main. It doesn't change the one in the outer scope. Look up shadowing.

This program demonstrates it well:

package main

import "fmt"

func main() {
    const a = 0
    fmt.Println(a)
    {
        const a = 1
        fmt.Println(a)
    }
    fmt.Println(a)
}

The output is as follows:

0
1
0