I think all of this will probably be handled with wrapper collections types and
the iterator pattern.
Generics should make this easy. It would be great is range supported this but
it seems doubtful.
> On Nov 12, 2021, at 10:37 AM, 'Axel Wagner' via golang-nuts
> <golang-nuts@googlegroups.com> wrote:
>
>
> It is still a different operation. For example, a range over a map is not
> necessarily deterministic.
>
> If you continue to ask detail-questions like this, it would be useful if you
> could provide an actual program you'd want to write using them. Otherwise, it
> makes a lot more sense to just wait for the spec-changes to be known. At that
> point, it'll be easier to talk about if a specific example does or does not
> conform to the spec.
>
>> On Fri, Nov 12, 2021 at 5:08 PM T L <tapir....@gmail.com> wrote:
>>
>>
>>> 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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