douyan8772 2014-07-27 14:10
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去:错误变量重新分配,正确使用?

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?

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  • douxin2003 2014-07-27 14:20
    关注

    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)
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

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