英文:
Go: error variable reassigning, proper use?
问题
我对Go语言中错误变量err的重新赋值感到困惑。
例如，我倾向于这样做：
err1 := Something()
checkErr(err1)
str, err2 := SomethingElse()
checkErr(err2)
err3 := SomethingAgain()
checkErr(err3)
但是我总是迷失其中，有成千上万个无用的err变量漂浮在代码中，而且这使得代码变得混乱和令人困惑。
但是如果我这样做：
err := Something()
checkErr(err)
str, err := SomethingElse()
checkErr(err)
err := SomethingAgain()
checkErr(err)
...它会报错说err已经被赋值。
但是如果我这样做：
var err error
err = Something()
checkErr(err)
str, err = SomethingElse()
checkErr(err)
err = SomethingAgain()
checkErr(err)
...它不起作用，因为str需要使用:=进行赋值。
我是不是漏掉了什么？
英文:
I'm confusing about the reassignment of the err variable for errors in Go.
For example, I tend to be doing this:
err1 := Something()
checkErr(err1)
str, err2 := SomethingElse()
checkErr(err2)
err3 := SomethingAgain()
checkErr(err3)
But I'm always losing track of this and have millions of useless err variables floating around that I don't need, and it makes the code messy and confusing.
But then if I do this:
err := Something()
checkErr(err)
str, err := SomethingElse()
checkErr(err)
err := SomethingAgain()
checkErr(err)
...it gets angry and says err is already assigned.
But if I do this:
var err error
err = Something()
checkErr(err)
str, err = SomethingElse()
checkErr(err)
err = SomethingAgain()
checkErr(err)
...it doesn't work because str needs to be assigned with :=
Am I missing something?
答案1
得分: 4
你快要完成了...在:=的左侧至少需要有一个新创建的变量。但是如果你没有提前声明err，编译器会尝试在每个:=的实例上创建它，这就是为什么你会得到第一个错误。所以这个例子可以工作，例如：
package main
import "fmt"
func foo() (string, error) {
return "Bar", nil
}
func main() {
var err error
s1, err := foo()
s2, err := foo()
fmt.Println(s1, s2, err)
}
或者在你的情况下：
//我们先声明它
var err error
//这是一个普通的赋值
err = Something()
checkErr(err)
//在这里，编译器知道只有str是一个新声明的变量
str, err := SomethingElse()
checkErr(err)
//再次...
err = SomethingAgain()
checkErr(err)
英文:
you're almost there... at the left side of := there needs to be at least one newly create variable. But if you don't declare err in advance, the compiler tries to create it on each instance of :=, which is why you get the first error. so this would work, for example:
package main
import "fmt"
func foo() (string, error) {
return "Bar", nil
}
func main() {
var err error
s1, err := foo()
s2, err := foo()
fmt.Println(s1,s2,err)
}
or in your case:
//we declare it first
var err error
//this is a normal assignment
err = Something()
checkErr(err)
// here, the compiler knows that only str is a newly declared variable
str, err := SomethingElse()
checkErr(err)
// and again...
err = SomethingAgain()
checkErr(err)
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