英文:
"err declared but not used" with multiple errors
问题
如果我有这样一个程序：
package main
import "strconv"
func main() {
a, err := strconv.Atoi("100")
println(a)
}
我得到了预期的结果：
.\file.go:5:7: err declared but not used
然而，这个程序：
package main
import "strconv"
func main() {
a, err := strconv.Atoi("100")
if err != nil {
panic(err)
}
b, err := strconv.Atoi("100")
println(a, b)
}
编译时没有错误，即使我从未检查过第二个 err 值。为什么会这样？另外，我能改变一些选项，使得这些错误导致编译时的错误或警告吗？
英文:
If I have a program like this:
package main
import "strconv"
func main() {
a, err := strconv.Atoi("100")
println(a)
}
I get this result, as expected:
.\file.go:5:7: err declared but not used
However this program:
package main
import "strconv"
func main() {
a, err := strconv.Atoi("100")
if err != nil {
panic(err)
}
b, err := strconv.Atoi("100")
println(a, b)
}
Compiles without error, even though I never checked the second err value. Why does this happen? Also, can I change some option, so that these mistakes result in compile time errors or warnings?
答案1
得分: 4
这是因为在第二种情况下，您正在重复使用现有的 err 变量，所以它被使用了。尽管使用了 := 实例化和赋值运算符，但并没有实例化一个新的 err 变量。
如果您将错误命名为不同的变量，例如：
func main() {
a, err := strconv.Atoi("100")
if err != nil {
panic(err)
}
b, err2 := strconv.Atoi("100")
println(a, b)
}
那么您将在两种情况下都会看到编译错误。
如果您不想更改代码但仍然希望收到此问题的通知，您将需要依赖于 Go 语言的一个 linter 而不是 Go 编译器。Go 有一个非常强大的 linter 生态系统，所以我不会推荐特定的一个，但在我们的组织中，如果我编写了这样的代码，我们的 linter 将会显示类似于以下错误：
scratch/test.go:10:2: ineffectual assignment to err (ineffassign)
b, err := strconv.Atoi("100")
英文:
This is because in the second case you are re-using an existing err variable, so it is being used. Despite the := instantiate & assign operator, a new err variable is not instantiated.
If you named the errors differently, such as this:
func main() {
a, err := strconv.Atoi("100")
if err != nil {
panic(err)
}
b, err2 := strconv.Atoi("100")
println(a, b)
}
Then you would see a compile error for both cases.
If you don't want to change your code but also still want to be notified of this issue, you will need to rely on a go linter instead of the go compiler. Go has a very robust ecosystem of linters so I won't recommend one in particular, but at my organization I would see an error like this from our linter if I were to write such code:
scratch/test.go:10:2: ineffectual assignment to err (ineffassign)
b, err := strconv.Atoi("100")
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