go - 在检查if-else条件时 undefined variable 名

Question

从教程中学习时，我编写了以下程序。这是关于检查go中的条件。
但是，它将作为undefined message抛出错误。请帮忙。

// Check out various conditional operators

package main

import "fmt"

func condition(x int) string {
    if x > 5 {
        message := "x is greater than 5"
    } else if x == 5 {
        message := "x is equal to 5"
    } else {
        message := "x is less than 5"
    }
    return message  // error on this line
}

func main() {
    x := 10 - 5
    msg := condition(x)
    fmt.Println("%s", msg)
}

输出接收为:

user$ go run conditionals.go 
# command-line-arguments
./conditionals.go:15:9: undefined: message

Answer 1

message的作用域在每个if / else分支中。您希望它的作用范围是功能级别:

func condition(x int) string {
    var message string
    if x > 5 {
        message = "x is greater than 5"
    } else if x == 5 {
        message = "x is equal to 5"
    } else {
        message = "x is less than 5"
    }
    return message
}

由于您要返回此值，因此您可以更新函数签名以包含返回的变量，例如

func condition(x int) (m string) {

    if x > 5 {
        m = "x is greater than 5"
    }
    // ...

    return // implicitly returns m value
}