从函数返回多个值

huangapple go评论85阅读模式
英文:

Returning multiple values from function

问题

我有这个函数:

func GetBasicAuth(w http.ResponseWriter, r *http.Request) (string, error) {
    secret, _, ok := r.BasicAuth()
    if !ok {
        return "", err //这样写对吗?
    }
    return secret, nil
}

我不得不声明这个函数将返回一个字符串和一个错误,但实际上它将返回其中之一。如果BasicAuth函数的ok值为false,那么我没有字符串可以返回,那么在这种情况下我该怎么办 - 只是返回一个空字符串吗?这看起来很奇怪!

英文:

I have this function:

func GetBasicAuth(w http.ResponseWriter, r *http.Request) (string, error) {
    secret, _, ok := r.BasicAuth()
    if !ok {
        return "", err //is this right?
    }
    return secret, nil
}

I've had to declare that the function will return a string and an error but in reality it will return one or the other. If the BasicAuth function wasn't ok then I have no string to return so what do I do here - just send an empty string? This seems weird!

答案1

得分: 2

除非另有说明(例如io.Reader),在Go语言中,返回a, b, c, …, error的函数/方法通常会期望如果err != nil,则所有其他返回值都是未定义的,不应使用或检查。通常(但不是必须的),当返回错误时,函数/方法会使用那些其他返回值的零值

正如前面提到的,一些函数/方法(例如io.ReaderRead(p []byte) (n int, err error))明确说明了其他行为:

在考虑错误err之前,调用者应始终处理返回的n > 0个字节。

而且,你创建的任何返回有用值的函数/方法,即使在某些错误情况下,也应该明确说明。

英文:

Unless documented otherwise (e.g. io.Reader),
it's normal for Go functions/methods returning a, b, c, …, error to expect that if err != nil that all other returned values are undefined and should not be used/examined.
It's usual (but not required) that when returning an error
the function/method uses whatever the zero value is for those other return values.

As mentioned, some functions/methods such as an io.Reader's Read(p []byte) (n int, err error) explicitly state other behaviour:
>Callers should always process the n > 0 bytes returned before
considering the error err.

And any functions/methods you create that return useful values even in the case of (some) errors should probably explicitly state that.

huangapple
  • 本文由 发表于 2015年5月23日 23:45:19
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