Thanks reply, I know *range expression is evaluated once before beginning
the loop, *but I delete map in for statements also really affected the
loop. why not set to nil can't affect real map.
func mapTest() {
m := map[int]int{1: 1, 2: 2}
for k, v := range m {
println(k, v)
delete(m, 2)
// m = nil
}
}
// output:
// 1 1
On Tuesday, January 16, 2018 at 10:48:45 AM UTC+8, Kevin Powick wrote:
>
>
>
> On Monday, 15 January 2018 21:23:40 UTC-5, sheepbao wrote:
>>
>> I wrote this code, and why `map=nil` don't stop the loop?
>> ```go
>>
>> func mapTest() {
>>
>> m := map[int]int{1: 1, 2: 2}
>>
>> for k, v := range m {
>>
>> println(k, v)
>>
>> m = nil
>>
>> }
>>
>> }
>>
>> ```
>>
>> output:
>>
>> 1 1
>>
>> 2 2
>>
>>
>> I don't understand when I set `m = nil`, the loop is not stop. m doesn't
>> seem to be affected.
>>
>
> https://golang.org/ref/spec#For_statements
>
>
> *The range expression is evaluated once before beginning the loop, with
> one exception: if the range expression is an array or a pointer to an array
> and at most one iteration variable is present, only the range expression's
> length is evaluated; if that length is constant, by definition the range
> expression itself will not be evaluated. *
>
>
>
> --
> Kevin Powick
>
>
>
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