Re: Declaring super types

On Apr 19, 9:16 am, David BL <davi..._at_iinet.net.au> wrote:
> On Apr 19, 8:23 pm, Nilone <rea..._at_gmail.com> wrote:
>
> > How would you want to use that relationship? Any examples to study?
>
> For example, functions that accept RATIONAL values could be passed
> values of type INTEGER.
>
> It’s quite useful. E.g. even in a low level language like C there are
> handy conversions amongst the built-in types:
>
> double sqrt(double);
>
> double x = sqrt(4); // integer 4 has implicit conversion to double
>
> BTW C++ allows one to write user-defined value types supporting
> implicit conversion from builtin-types, by writing single argument
> constructors. Actually I just posted to comp.lang.c++.moderated
> asking whether it can be regarded as a general purpose approach to
> value subtyping in that language. But it does seem strange for a type
> to declare itself as a supertype of another type.

As you've already pointed out, conversions neither require sub/ super/duper typing nor do they define them. Such "inheritance" notions get in the way of clear thinking far more than they help (actually that's true of most hierarchal notions to begin with).

In other words, totally drop these notions of sub/super/duper type and most if not everything is simpler and more clear. In this specific case there would simply be a function signature

   () : INTEGER -> RATIONAL declared somewhere with some name or anonymous as above that defines a coercion for this multi-sorted algebra. That is it. No more, no less, no need for sub/super/duper thinking at all.

C++ let's one think this way /most/ of the time (thanks to overloading, template, etc). Unfortunately some operators must be member functions which is an annoying asymmetry.

KHD PS. The "no names allowed" thread became a total annoying mess as soon as ill-defined nearly useless sub/super/duper language crept in. (Not to say it wasn't on the verge of mess from the very start ;-). Received on Mon Apr 19 2010 - 20:07:31 CEST