英文:
Go Compilation Error: Declared but not used (Although used)
问题
我有以下的Go示例代码：
package main
import (
"fmt"
"log"
"os"
"strconv"
)
func main() {
numberOfUsers := 10
numberOfUsersStr, found := os.LookupEnv("NUMBER_OF_USERS")
if found {
numberOfUsers, err := strconv.Atoi(numberOfUsersStr)
if err != nil {
log.Fatalln(err)
}
}
fmt.Printf("Number of users: %d", numberOfUsers)
}
在构建这段代码时，我遇到了以下错误：
> go build -o app .
.\app.go:14:3: numberOfUsers declared but not used
显然，该变量在最后的打印语句中被使用了，但它似乎被编译器隐藏了。我错过了什么？
英文:
I have the following Go example:
package main
import (
"fmt"
"log"
"os"
"strconv"
)
func main() {
numberOfUsers := 10
numberOfUsersStr, found := os.LookupEnv("NUMBER_OF_USERS")
if found {
numberOfUsers, err := strconv.Atoi(numberOfUsersStr)
if err != nil {
log.Fatalln(err)
}
}
fmt.Printf("Number of users: %d", numberOfUsers)
}
When building this snipper, I get the following error:
> go build -o app .
.\app.go:14:3: numberOfUsers declared but not used
Clearly the variable is used in the last print statement, however it seems hidden from the compiler. What am I missing?
答案1
得分: 1
当使用:=时，你正在声明一个新的变量。这意味着这里的numberOfUsers：
numberOfUsers, err := strconv.Atoi(numberOfUsersStr)
实际上是遮蔽了你的另一个numberOfUsers变量。
你可以通过事先声明err，然后使用=而不是:=来修复它，这样你只是给变量赋一个新值，而不是声明一个新变量。
var err error
numberOfUsers, err = strconv.Atoi(numberOfUsersStr)
英文:
When using :=, you're declaring a new variable. That means the numberOfUsers here:
numberOfUsers, err := strconv.Atoi(numberOfUsersStr)
is actually shadowing your other numberOfUsers variable.
You can fix it by declaring err beforehand and then using just = instead of := so that you are only assigning a new value to the variable and not declaring a new variable.
var err error
numberOfUsers, err = strconv.Atoi(numberOfUsersStr)
答案2
得分: 0
这行代码中的numberOfUsers变量未被使用：numberOfUsers, err := strconv.Atoi(numberOfUsersStr)。
在这里，你在if语句的作用域中重新声明了一个新的变量numberOfUsers。这个变量在该作用域中没有被使用，因此会出现错误。
你可能想要像这样修改代码：
func main() {
numberOfUsers := 10
numberOfUsersStr, found := os.LookupEnv("NUMBER_OF_USERS")
if found {
var err error
numberOfUsers, err = strconv.Atoi(numberOfUsersStr)
if err != nil {
log.Fatalln(err)
}
}
fmt.Printf("用户数量：%d", numberOfUsers)
}
请注意:=（声明并赋值一个新变量）和=（仅赋值）之间的区别。
英文:
The numberOfUsers variable in this line is unused: numberOfUsers, err := strconv.Atoi(numberOfUsersStr).
Here you are redeclaring a new variable numberOfUsers in the scope of the if statement. This variable is not used in that scope, hence the error.
You probably want something like this:
func main() {
numberOfUsers := 10
numberOfUsersStr, found := os.LookupEnv("NUMBER_OF_USERS")
if found {
var err error
numberOfUsers, err = strconv.Atoi(numberOfUsersStr)
if err != nil {
log.Fatalln(err)
}
}
fmt.Printf("Number of users: %d", numberOfUsers)
}
Notice the difference between := (declare an assign a new variable) and = (only assign).
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