On Tue, Aug 4, 2020 at 9:19 PM Robert Engels <reng...@ix.netcom.com> wrote:
>
> 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.
Numbers are not the only primitive types in Go.
Ian
> > 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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>
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