Re: Announce: Grace project site operational

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Wed, 22 May 2002 11:40:35 +0000 (UTC), Georg Bauhaus
<sb463ba@l1-hrz.uni-duisburg.de> wrote:

>Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
>
>:  C++ templates are simply untyped, substitute'n'pray.
>
>Is this a general statement? Out of couriosity:
>
template <
  class Thing,
[ ... example skipped ]
>
>g++ -c test.cc
>test.cc: In function
>	`int oodle<does_not_have_plus, 9, clrkpt>(does_not_have_plus)':
>test.cc:24:   instantiated from here
>test.cc:7: no match for `does_not_have_plus & + int'
>
>So (lack of C++ template understanding on my side not withstanding)
>there are cases where a prayer isn't needed?

I did not claimed that C++ is untyped. I claimed that the formal
template parameters are untyped in the sense that you cannot say:

template <class Thing that has +,

This requirement cannot be made a part of the contract. The contract
is as simple as "any type that makes macro expansion a valid program".
It is not much better than: #define private public. So far the result
remains a valid programs it is fine! That actual has or has not plus
will be checked in C++ only after substitution. One need body to check
that! Consider that somebody has instantiated your template, but did
not use the bodies where + is used. No error, though the contract is
broken. Well, after 10 years or so, somebody would try to use that
bodies and run at misterious errors in the code which is supposed to
be safe. In Ada at least one can write:

generic
   type Thing is new Field with private; -- Field has "+"

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de