On Thu, Aug 6, 2020 at 1:17 PM Ian Lance Taylor <i...@golang.org> wrote:
>
> On Thu, Aug 6, 2020 at 12:10 PM Robert Engels <reng...@ix.netcom.com> wrote:
> >
> > We’ll probably agree to disagree there. Java has a lot of generic code
> > written and it’s never been a problem (using methods). Rarely can you write
> > code that treats + the same no matter if passed a string or numeric.
> >
> > Even operators like < with strings don’t really make a lot of sense because
> > different collations are used.
> >
> > I think having a higher bar for Go generic implementations is fine -
> > writing generic code properly is harder than regular Go - there’s much more
> > to resin about.
>
> I hope that is not the case.
>
> Also, it's important that it be easy to read generic code. We can put
> extra burdens on writers of generic code if necessary, but we must
> make the burden on readers of generic code as small as we possibly
> can.
>
> And again: is the complexity from requiring methods rather than
> operators really less than the complexity of using type lists?
There are things you can do with type lists that you cannot do with
operators. You can limit a function to run on unsigned numbers, for
instance. I think it also makes it explicit to the reader that
a.Add(b) is possibly more complicated than a+b.
>
> Ian
>
>
>
> > > On Aug 6, 2020, at 1:53 PM, Ian Lance Taylor <i...@golang.org> wrote:
> > >
> > > On Wed, Aug 5, 2020 at 8:52 PM Robert Engels <reng...@ix.netcom.com>
> > > wrote:
> > >>
> > >> I understand your point, but I think a few minor corrections Make a
> > >> difference - it does not matter that String supports + and not - , a
> > >> string would not be a Number. String concatenation is not addition.
> > >
> > > My point wasn't that a string is a number. My point was that the
> > > current design draft permits writing a function that uses + and works
> > > with both strings and numbers. If we adopt something along the lines
> > > of what you are suggesting, we must either define a name for "types
> > > that support +" or we must say "you can't write a generic function
> > > that uses + and works with both strings and numbers."
> > >
> > >
> > >> There are also several ways to implement “ordering” with complex
> > >> numbers, even between complex and rational - it’s all a matter of
> > >> definition. There is also the possibility to make complex not a
> > >> Comparable (compile time failure).
> > >
> > > In Go, the types complex64 and complex128 do not support the < <= >= >
> > > operators. That is what I mean when I say that the complex types are
> > > not ordered. I'm not sure it matters that it is possible to define
> > > some ordering on complex numbers; the point is that the language
> > > defines no such ordering, so if you need to use ordering operators you
> > > can't use complex types.
> > >
> > >
> > >> You write the generic code using methods not operators in all cases.
> > >
> > > Ah, I didn't understand that. I think that is a non-starter. I think
> > > it is a requirement that people be able to write (and read) Min as
> > >
> > > if a < b {
> > > return a
> > > }
> > > return b
> > >
> > > Saying that you must write this as, e.g.,
> > >
> > > if a.Less(b) {
> > > return a
> > > }
> > > return b
> > >
> > > means that the generic language is not the normal language. That adds
> > > a massive layer of complexity to using generics: you can no longer
> > > write ordinary Go code for generic functions, you have to write in
> > > this alternative language that is harder to write and harder to read.
> > > You also have to remember a bunch of names for the methods that
> > > correspond to the operators. The design draft works very hard to
> > > avoid these issues.
> > >
> > > In particular, I think that making that requirement would be adding
> > > much more complexity to the language than we get by adding type lists.
> > >
> > > Ian
> >
>
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