Re: Ada Generic vs. C++ Templates

[Colin_Paul_Gloster@ACM.org (Colin Paul Gloster)]

In article <3ACD1045.E9ECB65F@worldnet.att.net>, James Rogers wrote:
"DuckE wrote:
> 
> You have implied that GNAT implements the entire Ada95 standard.
> 
> While all of the "required" elements are supported, some things are not.
> 
> Just try making use of "Ada.Asynchronous_Task_Control" and you'll get a
> message:
>   Asynchonnous_Task_Control is not implemented.

This, of course, does not even approach the problems found with C++
compilers.

I am sure you will correct me if I am wrong in this. I believe the C++
standard contains no optional annexes."

Probably true that it has no optional annexes.

"GNAT does implement all required features of the Ada language, and
nearly every feature of the optional annexes. You cannot write an Ada
program that compiles in GNAT, using only required features of the 
language, and not successfully compile the same program using another
Ada compiler.

On the other hand, you can easily write a C++ program using the
Microsoft C++ compiler that will not compile properly using the
Watcom C++ compiler."

Watcom having gone bust before the Standard came to be. As for those
current Standard-sriving compilers, your point holds. There are people
who care though and do get more than one C++ compiler to successfully
compile the same source.

"The C++ reference manual is larger than the Ada reference manual.
This is only important as an indication of the difficulty of
compiler implementation implied by the size of the document. You
may deny the validity of this measure,"

I agree that it is indicative. Something I do not like is people
referencing "The C++ Programming Language" (or the second edition of 
"The C Programming Language", 1988, Prentice Hall in the case of C89 when
C89 was Standard C) as authoriative when they are not prescriptive -- the
Standard is the authority. Note even that "The C Programming
Language" predates the ex-standard people incorrectly throw it around as
defining and is based on a late draft standard.

It may be worth mentioning that staff writers for "C/C++ User's
Journal" have said things along the lines of such and such seems to be
the case in Standard C++, evidence to support said opinion (note
opinion and evidence, not things they are billing as definitely
correct interpretations of the Standard) being from whatever section (of
the actual Standard thank goodness). The editor said that because of such
common referrals to the C++ Standard in CUJ, the Standard is
excellent. Merely on that measure the opposite is a far more sensible
suspicion.

"but the current lack of compilers implementing the standard speaks
loudly to me. It must be due to the standard itself."

Yes. Note however that on average the greatest deficiencies in
completely implementating it seems to be in finishing off the
libraries. Libraries are not so much a language issue. Still the actual
language implementations have some way to go yet.

"The C++ language standard has too often ignored the concerns of compiler
writers. Features and language definitions have been placed in the
standard to satisfy application developers without proper concern for the
need to implement those features in a compiler."

My reaction to this makes me feel that it is grossly untrue.
Colin Paul
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