On Friday, November 12, 2021 at 6:07:11 PM UTC+8 axel.wa...@googlemail.com
wrote:
> And FWIW, just to illustrate the expected complexity: We also want these
> two declarations to mean the same:
> func A[T A]()
> func B[T interface{ A }]()
> So the rules also need to accommodate that. It gets only more complicated
> from there.
>
Are the followings also intended?
func Foo[T any](T T) T { // (the 2nd) T redeclared in this block
return T // T (type) is not an expression
}
func Bar[T any](x T) T {
var T = x // T redeclared in this block
return T
}
>
> On Fri, Nov 12, 2021 at 11:03 AM Axel Wagner <axel.wa...@googlemail.com>
> wrote:
>
>>
>>
>> On Fri, Nov 12, 2021 at 10:54 AM tapi...@gmail.com <tapi...@gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Friday, November 12, 2021 at 5:33:19 PM UTC+8
>>> axel.wa...@googlemail.com wrote:
>>>
>>>> I suspect this issue is hard/impossible to avoid, because it must be
>>>> possible to self- and mutually reference type-parameters, in a way that
>>>> it's not for normal parameters, to allow to write something like
>>>>
>>>> type Equaler[T any] interface {
>>>> Equal(T) bool
>>>> }
>>>> func Eq[T Equaler[T]](a, b T) bool {
>>>> return a.Equal(b)
>>>> }
>>>>
>>>
>>> I don't see the same problem here. "T" and "Equaler" are two different
>>> identifiers.
>>>
>>
>> But T and T are not.
>>
>> The point I was making is that type-parameters must inherently be scoped
>> in a way that makes them visible in the type-list itself, to make writing
>> code like this possible. This isn't necessary for regular parameters and
>> it's what makes type-parameter lists special.
>>
>> I *also* said that it's probably possible to devise rules which would
>> make this possible, while allowing the example you wrote, just that those
>> rules would have to be complicated.
>>
>>
>>>
>>>
>>>>
>>>> or basically any use-case for constraint-type inference.
>>>>
>>>> Even if we *could* allow it consistently, the rules for doing that
>>>> would likely be pretty complex. Better to take the relatively minor hit of
>>>> disallowing this overloading (you can always use different names for the
>>>> type-parameters, if they conflict with the constraint you want to use)
>>>> than
>>>> to take the hit of complex scoping rules with lots of exceptions.
>>>>
>>>> On Fri, Nov 12, 2021 at 9:48 AM tapi...@gmail.com <tapi...@gmail.com>
>>>> wrote:
>>>>
>>>>> I expect the following code compilers okay, but it doesn't.
>>>>> It looks All the three "I" in the Bar function declaration are
>>>>> viewed as the type parameter, whereas the second one is
>>>>> expected as the constraint I (at least by me).
>>>>>
>>>>> package main
>>>>>
>>>>> type I interface { M() }
>>>>>
>>>>> func Foo(i I) {
>>>>> i.M()
>>>>> }
>>>>>
>>>>> func Bar[I I](i I) { // cannot use a type parameter as constraint
>>>>> i.M()
>>>>> }
>>>>>
>>>>> func main() {}
>>>>>
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>>>>> .
>>>>>
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>>>
>>
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