英文:
Why is it possible to declare the same var two times using for-loop?
问题
我正在为您翻译以下内容：
我正在尝试在http://tour.golang.org/上使用Go语言，并且我发现在for循环中可以使用:=声明两次相同的变量。
输出结果与Go编译器相同。
以下是我的测试代码：（请注意变量i被声明了两次）
package main
import "fmt"
func main() {
i := "Hello"
a := 0
for a < 2 {
fmt.Println(i)
i := "World !"
fmt.Println(i)
a++
}
}
输出结果：
Hello
World !
Hello
World !
有人可以解释一下这是为什么吗？
英文:
I was trying Go on http://tour.golang.org/, and I saw that it was possible to declarate two times the same var using := in for loop.
The output is the same with the Go compiler.
Here is my test : (see the var i, it was declared two times)
package main
import "fmt"
func main() {
i := "Hello"
a := 0
for a < 2 {
fmt.Println(i)
i := "World !"
fmt.Println(i)
a++
}
}
Output :
> Hello
>
> World !
>
> Hello
>
> World !
Can someone explain that ?
答案1
得分: 4
短变量声明 i := ... 会遮盖在 for 循环的**块**之外声明的同名变量。
> 每个“if”、“for”和“switch”语句都被视为自己的隐式块。
你可以在“Go gotcha #1: variable shadowing within inner scope due to use of := operator”中了解更多信息。
它参考了这个goNuts讨论。
短变量声明可以在一个块内重新声明同名变量，但由于 i 也在 for 块之外声明了（不同的作用域），它在该块之外保持其值。
英文:
The short variable declaration i := ... will overshadow the same variable declared outside of the scope of the for loop block.
> Each "if", "for", and "switch" statement is considered to be in its own implicit block
You can see more at "Go gotcha #1: variable shadowing within inner scope due to use of := operator"
It refers to this goNuts discussion.
A short variable declaration can redeclare the same variable within a block, but since i is also declared outside the for block, it keeps its value outside said block (different scope).
答案2
得分: 1
第一个i在main函数的大括号（{}）内部定义，而第二个i在for循环的作用域内声明。名称相同，但作用域不同。
英文:
The first i has been defined inside the braces ({}) of main function wheras the second i is declared within the scope of the for loop. The name is same but the scope is different.
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