Re: Ada generics

[Hyman Rosen <hyrosen@mail.com>]

Dmitry A. Kazakov wrote:
> Automatic conversions do not represent any special case. If S is
> convertible to T, then S is a subtype of T

That simply is not the case in C++. Automatic conversions do not
define subtypes in any meaningful or useful sense. For example,
all the numeric types automatically convert to each other. It's
also possible to write automatic conversions between arbitrary
classes. It may be chaotic as you say, but that's the way the
language is, and templates have to work within that framework.
"Concepts" will be useful to those people who want the ability to
specify such constraints.

> Exactly. The idea of structural matching is wrong.

It's not wrong, and it's not even structural. It is in fact
matching by name, not by structure. It's only in the case of
constant expressions that things go a little awry. But if you
recall the discussions we've had here on implementing units,
it lets C++ do things that are impossible in Ada.

> It is actually the difference between packages in Ada and classes in C++.
> They are not equivalent.

Not entirely, naturally, but classes in C++ are used for the same
kind of structuring purposes as Ada packages. Certainly C++ classes
are used to define bundles of types, constants, and functions, and
that can be done generically.