The operator support is what makes things so complicated. Why not define a
“numeric” type that has methods for all the operators that is used with
generics, similar to Number in Java. Then it is unified. If you are writing
specialized math performant code you would probably use concrete types anyway.
People complained about the boxing of primitives in Java but it was rarely a
problem in actual use - and then people fell back to specialized structures
anyway - which is what would happen here.
> On Aug 4, 2020, at 11:06 PM, Ian Lance Taylor <i...@golang.org> wrote:
>
> On Tue, Aug 4, 2020 at 7:31 PM Ben Hoyt <benh...@gmail.com> wrote:
>>
>>> Yes, I think that the ability to write generics using operators is not
>>> optional. As I've said before, there are some functions that must be
>>> possible to write using any plausible generics mechanism. One of them
>>> is the Min function that returns the smaller of two values of some
>>> ordered type. If we can't write that trivial function, our generics
>>> mechanism is not usable for practical code.
>>
>> I don't think that's quite true. You can write it, it's just not as
>> nice to use with builtin types:
>>
>> func Min[type T Lesser](a, b T) T {
>> if a.Less(b) {
>> return a
>> }
>> return b
>> }
>>
>> To use it with (for example) int, you need to write a wrapper type, for
>> example:
>>
>> type Int int
>> func (i Int) Less(j Int) bool { return i < j }
>>
>> And then call it like so:
>>
>> Min(Int(2), Int(3))
>>
>> It's not pretty, but it definitely works
>> (https://go2goplay.golang.org/p/i6Q3tF-QwgH). This was kind of the
>> situation with sort.Sort (until sort.Slice came along), so it doesn't
>> seem any worse than that. Or you could instead define a generic type
>> "Ord" instead of Int:
>>
>> type Ord[type T Ordered] T
>> func (i Ord[T]) Less(j Ord[T]) bool { return i < j }
>>
>> And use it like so:
>>
>> Min(Ord[int](2), Ord[int](3))
>>
>> Or if type inference were improved to handle that case:
>>
>> Min(Ord(2), Ord(3))
>>
>> It's not pretty, partly because you get an Int/Ord result instead of a
>> plain int, but not terrible either.
>>
>> So it seems to me it's not a case of "we can't write that trivial
>> function" -- it just requires a bit of type conversion.
>
> OK, fair enough.
>
> I'll be more specific: I think it's necessary that it be possible to
> write a Min function whose body is something similar to
>
> if a < b {
> return a
> }
> return b
>
> I think that any approach to generics that requires more complex code
> would simply be rejected by the community of Go programmers.
>
>
>> So either way
>> -- with your approach or this approach -- it's klunky for one of the
>> cases:
>>
>> 1) Assuming type lists and a function which takes a comparator func
>> like "func Min[type T](a, b T, less func(x, y T) bool) T" -- in this
>> case you have the klunkiness of having to import (or define)
>> "primitives" and specify the comparison func even when it's obvious:
>> Min(2, 4, primitives.Less)
>> 2) With no type lists and a function which takes a "lesser" like "func
>> Min[type T Lesser](a, b T) T" -- in this case you have the klunkiness
>> of having to use wrapper types, like we did with sort.Sort back in the
>> day.
>
> To be clear, when I discussed a function, I was only discussing that
> in contrast to a type with a required method. I did not mean to
> suggest that a function would be suitable for use with a primitive
> type that supports operators.
>
> Ian
>
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