已声明且未在条件语句中使用的变量 [英] Variable declared and not used in conditional statement

问题描述

我在条件语句之外声明了一些变量( offsetI 和 limitI ).在条件语句内部，我尝试为它们分配值，然后在条件语句之后将这些值用于查询.

I declare some variables (offsetI and limitI) outside of a conditional statement. Inside the conditional statement I am trying to assign them values, then use those values for a query after the conditional statement.

var (
    number, size, offset, limit string
    offsetI, limitI             uint64
)

// Get the string values for number, size, offset, and limit
// ...

if size != "" {

    // Parse the number value
    numberI, err := strconv.ParseUint(number, 10, 64)
    if err != nil {...}

    // Parse the size value
    limitI, err = strconv.ParseUint(size, 10, 64)
    if err != nil {...}

    // Calculate the offset
    offsetI = numberI * limitI

} else {

    // Parse the limit value
    limitI, err := strconv.ParseUint(limit, 10, 64)         // limitI declared and not used
    if err != nil {...}

    // Parse the offset value
    offsetI, err = strconv.ParseUint(offset, 10, 64)
    if err != nil {...}
}

// Make the query using offsetI and limitI
result, err := s.GetAllPaginated(offsetI, limitI)
if err != nil {...}

---

我不打算在 else 语句的范围内重新声明 limitI 变量，但是我需要使用:= 运算符，用于声明新的 err 变量.

---

I am not intending to re-declare the limitI variable in the scope of the else statement, but I need to use the := operator for declaring a new err variable.

我唯一能想到的就是分别声明另一个 err 变量，因此我可以使用常规的赋值语句:

The only thing I could come up with was to separately declare another err variable, so I could use a regular assignment statement:

} else {

    var err error    // New

    // Regular assignment statement now
    limitI, err = strconv.ParseUint(limit, 10, 64)
    if err != nil {...}

---

我希望能够不必声明其他错误变量就能做到这一点.

---

I would like to be able to do this without having to declare an additional error variable.

推荐答案

额外的 var错误很尴尬，但这是解决这种情况的常用方法.范围界定规范说(强调我):

The extra var error is awkward, but it's a common way to address this situation. The spec on scoping says (emphasis mine):

在函数内部声明的常量或变量标识符的范围始于ConstSpec或VarSpec的末尾(对于简短变量声明，为ShortVarDecl)，并终止于最内层的包含块的末尾./p>

因此，在您的情况下，简短的变量声明是声明一个 different limitI 范围为最内层的块".由于它只能生存"到下一个大括号，因此不会使用.

So in your case, that short variable declaration is declaring a different limitI scoped to the "innermost containing block." Since it only "lives" until the next closing brace, it isn't used.

在您的特定情况下，一个选项可能是在if/else之外声明 err ，因为这两个内部作用域都使用了它，因此您可以改用 = := 的代码，这些函数返回 error s.那么就没有声明内部 limitI "，并且您没有未使用的变量问题.

In your specific case, an option might be to declare err outside the if/else, since it's used in both inner scopes, so you can use use = instead of := with those functions returning errors. Then there's no "inner limitI" declared and you have no unused variable issue.

像这样的阴影"情况也会产生意外的行为，而不是错误. go vet -shadow 尝试检测"[v]可能包含被无意间遮盖了" ，并且与此不同但又相关， gordonklaus/ineffasign 概括了未使用的变量"检查以检测无用的分配，即使它们不是声明.

"Shadowing" situations like this can also produce unexpected behavior rather than an error. go vet -shadow tries to detect "[v]ariables that may have been unintentionally shadowed" and, different but related, gordonklaus/ineffasign generalizes the "unused variable" check to detect useless assignments even if they weren't declarations.

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