> class <a:type> mysamepair(a): mypair(a, a) {
> method swap(): void = ...
> }
>
I feel that this is a serious problem with typed OOP. Let me
give another example which I think no current OOP syntax can
handle.
Say we have an object of the type myrectangle(x, y), where
x and y are of the sort int (for width and height). Imagine a method
for doubling the width:
fun
double_width
(obj: !myrectangle(x, y) >> myrectangle(2*x, y)): void
This cannot be handled with OOP syntax because OOP syntax all
implicitly assumes that the type of 'this' cannot be changed by a method
call.
Also, one cannot introduce mysquare(x) as a subclass of myrectangle(x, x)
because double_with turns a square (of non-zero length) into a non-square
rectangle.
--Hongwei
On Mon, Jan 18, 2021 at 3:51 AM Elijah Stone <elro...@elronnd.net> wrote:
> On Sun, 17 Jan 2021, gmhwxi wrote:
>
> > This time I would like to do something a bit more interesting:
> >
> > class
> > <a:type
> > , b:type>
> > mygpair(a, b)
> > *snip*
>
> Do we need to say both <a:type,b:type> and (a,b)? It seems redundant,
> since we already know the class is parametrized according to a and b, but
> maybe I'm missing something?
>
>
> > The mygpair(T1, T2) is a so-called generic class parameterized over
> > types T1 and T2. For an object of the type mygpair(T, T), a method for
> > swapping the fst and snd components of the object can be supported. But
> > this is difficult to do with the OOP syntax. BTW, how would be done in
> > Java? Such a method can be readily implemented with the following
> > syntax:
> >
> > fun
> > <a:type>
> > swap(pp: mygpair(a, a)): void =
> > let
> > val tmp = pp.fst in pp.fst := pp.snd; pp.snd := tmp
> > end
>
> Hmmm. In a language like c++ where templates are not checked until
> they're instantiated, you would be able to just make that a template
> method. That doesn't work so well in practice, however...
>
> One possible solution is subtyping. As in:
>
> class <a:type,b:type> mypair(a, b) {
> var fst: a
> var snd: b
> //...
> }
>
> class <a:type> mysamepair(a): mypair(a, a) {
> method swap(): void = ...
> }
>
> -E
>
> --
> You received this message because you are subscribed to a topic in the
> Google Groups "ats-lang-users" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/ats-lang-users/snZWQK2YePY/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> ats-lang-users+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/ats-lang-users/7e9a72f0-b2ee-af5f-b297-57f929179ebd%40elronnd.net
> .
>
--
You received this message because you are subscribed to the Google Groups
"ats-lang-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to ats-lang-users+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/ats-lang-users/CAPPSPLqCwvGL_2Um%2B45tZSW8HNA%3D4Rir2kTah-1oZNqRHz_Lbw%40mail.gmail.com.
