结构类型不可变

Question

I wrote a sample application about assign value to variable. Look at the following code snippet:

package main

import (
    "fmt"
)

func main() {

    cp := 344
    fmt.Println(cp)
    cp = 566565
    fmt.Println(cp)

    res := []struct {
        Email     string `json:"n.email"`
        Activated bool   `json:"n.activated"`
    }{}

    fmt.Println(res)

    res = []struct {
        Email string `json:"n.email"`
    }{}

    fmt.Println(res)
}

First cp variable, I assign value then after do it again and it works. At the end cp carry the value 566565. For me is int mutable.

The second code does not work, reassign new struct to res, I got compiler error.

./double_assignment.go:23: cannot use []struct { Email string } literal (type []struct { Email string }) as type []struct { Email string; Activated bool } in assignment

Is struct immutable?

Answer 1

The first short variable declaration res := did set a certain type ([]struct { Email string; Activated bool}).

If you want to assign a different type (here, a different struct literal []struct { Email string }), you need a different variable.

res2 = []struct {
        Email string `json:"n.email"`
}{}

fmt.Println(res2)

(as in play.golang.org )