On Fri, Nov 12, 2021 at 11:54 PM Axel Wagner <axel.wagner...@googlemail.com>
wrote:
> Oh, sorry, I just re-read. Your example still requires `range` to return
> distinct types, so that probably shouldn't work.
>
Not this reason:
func Bar[T []byte|map[int]byte](s T) {
for i, v := range s { _, _ = i, v} // cannot range over s (variable of
type T constrained by []byte|map[int]byte) (type set has no single
underlying type)
}
>
> On Fri, Nov 12, 2021 at 4:52 PM Axel Wagner <axel.wagner...@googlemail.com>
> wrote:
>
>> The error message gives you a reason - there is no single underlying
>> type. This works:
>>
>> type B []byte
>> func Bar[T []byte|B](s T) {
>> for range s {}
>> }
>>
>> But yes, your example arguably should be made to work eventually. I would
>> suggest filing an issue about that.
>>
>> On Fri, Nov 12, 2021 at 4:47 PM tapi...@gmail.com <tapir....@gmail.com>
>> wrote:
>>
>>> This one doesn't compile either.
>>> So the range operation doesn't support values of parameter types?
>>>
>>> type MyByte byte
>>>
>>> func Bar[T []byte|[]MyByte](s T) {
>>> for range s {} // cannot range over s (variable of type T
>>> constrained by []byte|[]MyByte) (type set has no single underlying
>>> }
>>>
>>> On Friday, November 12, 2021 at 11:40:53 PM UTC+8
>>> axel.wa...@googlemail.com wrote:
>>>
>>>> On Fri, Nov 12, 2021 at 4:29 PM tapi...@gmail.com <tapi...@gmail.com>
>>>> wrote:
>>>>
>>>>> On Friday, November 12, 2021 at 11:10:17 PM UTC+8
>>>>> axel.wa...@googlemail.com wrote:
>>>>>
>>>>>> `range s` works differently for string and []byte. In the former case
>>>>>> it iterates over utf8-encoded unicode codepoints, in the latter it
>>>>>> iterates
>>>>>> over bytes.
>>>>>>
>>>>>
>>>>> It is true, but why it matters here?
>>>>>
>>>>
>>>> Because it makes `range` different operations for the purposes of
>>>> determining the allowed operations on a type-parameter.
>>>>
>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> On Fri, Nov 12, 2021 at 3:18 PM tapi...@gmail.com <tapi...@gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> func Bar[T []byte|string](s T) bool {
>>>>>>> for _, v := range s { // cannot range over s (variable of type T
>>>>>>> constrained by []byte|string) (T has no structural type)
>>>>>>> if v > 100 {
>>>>>>> return true
>>>>>>> }
>>>>>>> }
>>>>>>> return false
>>>>>>> }
>>>>>>>
>>>>>>> The message is quite confusing.
>>>>>>>
>>>>>>> --
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>>>>>>> .
>>>>>>>
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>>>>> .
>>>>>
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>>> .
>>>
>>
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