A parameterized class (i.e. template class / class template) is not a class?

[christopher diggins]

It appears that the following is not considered a class:

template<typena me T>
class C { };

?

So officially is this considered: a class, a template, a class template, or
a template class? I always thought of it as a parameterized class. What
would the rationale be for not considering it as just a 'class'?

--
Christopher Diggins
Object Oriented Template Library (OOTL)

http://www.ootl.org

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

christopher diggins wrote:[color=blue]
> It appears that the following is not considered a class:
>
> template<typena me T>
> class C { };
>
> ?
>
> So officially is this considered: a class, a template, a class template, or
> a template class? I always thought of it as a parameterized class. What
> would the rationale be for not considering it as just a 'class'?
>[/color]

It's not a class because you can't define objects of type C. It's a
class template, because it defines a pattern for creating classes.
C<int> is a class.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Howard]

Re: A parameterized class (i.e. template class / class template) is not a class?


"christophe r diggins" <cdiggins@video tron.ca> wrote in message
news:CONde.4379 9$SI2.1069666@w agner.videotron .net...[color=blue]
> It appears that the following is not considered a class:
>[/color]

By whom?
[color=blue]
> template<typena me T>
> class C { };
>
> ?
>
> So officially is this considered: a class, a template, a class template,
> or a template class? I always thought of it as a parameterized class. What
> would the rationale be for not considering it as just a 'class'?
>[/color]

I see no such rationale.

Obviously, it's a template. What type of template?... a class template (as
opposed to, say, a function template), since it defines a class.

Also obviously (to me), it's a class, since it defines a class. I don't
know if it's correct terminology, but I often refer to it as a template
class, as in "a class that is described by a template".

But I believe that the "correct" terminology is "class template".

Is this question because one poster suggested there was no string class in
standard C++? If so, I'd ignore that statement and get on with things.
It's probably irrelevant in the long run, as long as someone you're
communicating with understands what you're trying to say.

-Howard

[Howard]

Re: A parameterized class (i.e. template class / class template) is not a class?


"Pete Becker" <petebecker@acm .org> wrote in message
news:-MadneWk_N-CNurfRVn-pg@rcn.net...[color=blue]
> christopher diggins wrote:[color=green]
>> It appears that the following is not considered a class:
>>
>> template<typena me T>
>> class C { };
>>
>> ?
>>
>> So officially is this considered: a class, a template, a class template,
>> or a template class? I always thought of it as a parameterized class.
>> What would the rationale be for not considering it as just a 'class'?
>>[/color]
>
> It's not a class because you can't define objects of type C. It's a class
> template, because it defines a pattern for creating classes. C<int> is a
> class.
>[/color]

Good point. I agree, (and take back my remark that C itself is a class).

-Howard

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

Howard wrote:[color=blue]
>
> Is this question because one poster suggested there was no string class in
> standard C++?
>[/color]

Maybe, but that statement is wrong. There's the basic_string class
template (which we've established is not a class <g>), and there's the
typedef string, which is a class.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Abecedarian]

Re: A parameterized class (i.e. template class / class template) is not a class?

Pete Becker wrote:[color=blue]
> Howard wrote:[color=green]
> >
> > Is this question because one poster suggested there was no string[/color][/color]
class in[color=blue][color=green]
> > standard C++?
> >[/color]
>
> Maybe, but that statement is wrong. There's the basic_string class
> template (which we've established is not a class <g>), and there's[/color]
the[color=blue]
> typedef string, which is a class.[/color]

Let me add something to the confusion:[color=blue]
>From the C++ Standard, 7.1.3 The typedef specifier: "A typedef-name is[/color]
thus a synonym for another type. A typedef-name does not introduce a
new type the way a class declaration (9.1) or enum declaration does."
Also, an instantiated class template has different code generation
rules (not all functions are created) and different lookup rules (e.g.
dependent names) ...
If it were not different it would be the same ;-)

Abe

[Victor Bazarov]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:[color=blue]
> Pete Becker wrote:
>[color=green]
>>Howard wrote:
>>[color=darkred]
>>>Is this question because one poster suggested there was no string[/color][/color]
>
> class in
>[color=green][color=darkred]
>>>standard C++?
>>>[/color]
>>
>>Maybe, but that statement is wrong. There's the basic_string class
>>template (which we've established is not a class <g>), and there's[/color]
>
> the
>[color=green]
>>typedef string, which is a class.[/color]
>
>
> Let me add something to the confusion:[color=green]
>>From the C++ Standard, 7.1.3 The typedef specifier: "A typedef-name is[/color]
> thus a synonym for another type. A typedef-name does not introduce a
> new type the way a class declaration (9.1) or enum declaration does."
> Also, an instantiated class template[/color]

What is "an instantiated class template"? You mean an instantiation of
a class template?..
[color=blue]
> has different code generation
> rules (not all functions are created) and different lookup rules (e.g.
> dependent names) ...
> If it were not different it would be the same ;-)[/color]

I am not sure how this "adds to the confusion"? 'std::string' is merely
a synonym for 'std::basic_str ing<char>'. The latter is a class. So is
'string'. I am not sure what it has to do with code generation rules or
the lookup rules. It's a class as far as classes are concerned in the
"class template versus class" context.

V

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:[color=blue]
> Pete Becker wrote:
>[color=green]
>>Howard wrote:
>>[color=darkred]
>>>Is this question because one poster suggested there was no string[/color][/color]
>
> class in
>[color=green][color=darkred]
>>>standard C++?
>>>[/color]
>>
>>Maybe, but that statement is wrong. There's the basic_string class
>>template (which we've established is not a class <g>), and there's[/color]
>
> the
>[color=green]
>>typedef string, which is a class.[/color]
>
>
> Let me add something to the confusion:[/color]

No, please don't. <g> string is a typedef for basic_string<ch ar>, which
is a class. Yes, the rules are somewhat different, but the point is that
it names a type. Don't get carried away with fine-tuning terms so that
they become hard to use.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Abecedarian]

Re: A parameterized class (i.e. template class / class template) is not a class?

Pete Becker wrote:[color=blue]
> string is a typedef for basic_string<ch ar>, which
> is a class. Yes, the rules are somewhat different, but the point is[/color]
that[color=blue]
> it names a type. Don't get carried away with fine-tuning terms so[/color]
that[color=blue]
> they become hard to use.[/color]

One last wish since you are the right addressee. I'd appreciate if the
C++ Standard allowed a "real" string class alternatively to a typedef
std::basic_stri ng<char, ...> string "class". Usability would be
improved significantly at virtually no cost and 100% backward
compatibility.

Regards,
Abe

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:[color=blue]
>
> One last wish since you are the right addressee. I'd appreciate if the
> C++ Standard allowed a "real" string class alternatively to a typedef
> std::basic_stri ng<char, ...> string "class". Usability would be
> improved significantly at virtually no cost and 100% backward
> compatibility.
>[/color]

How would a "real" string class differ from basic_string<ch ar>?

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Abecedarian]

Re: A parameterized class (i.e. template class / class template) is not a class?

Pete Becker wrote:[color=blue]
> Abecedarian wrote:[color=green]
> >
> > One last wish since you are the right addressee. I'd appreciate if[/color][/color]
the[color=blue][color=green]
> > C++ Standard allowed a "real" string class alternatively to a[/color][/color]
typedef[color=blue][color=green]
> > std::basic_stri ng<char, ...> string "class". Usability would be
> > improved significantly at virtually no cost and 100% backward
> > compatibility.
> >[/color]
>
> How would a "real" string class differ from basic_string<ch ar>?[/color]

namespace std {
class string { /* interface as basic_string template */ };
}

This class would be much more convenient for the user than a template
with 3 parameters. The verbosity of error messages could be reduced to
a fraction of basic_string, even more when string is used as template
in other templates.

Regards,
Abe

[Victor Bazarov]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:[color=blue]
> [..]
> namespace std {
> class string { /* interface as basic_string template */ };
> }
>
> This class would be much more convenient for the user than a template
> with 3 parameters. The verbosity of error messages could be reduced to
> a fraction of basic_string, even more when string is used as template
> in other templates.[/color]

This should be solved by the compiler implementors, not by making changes
to the library. A simple feature: if a typedef is in scope, use it when
emitting an error message or a warning instead of full template spec.

V

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:
[color=blue]
>
> namespace std {
> class string { /* interface as basic_string template */ };
> }
>
> This class would be much more convenient for the user than a template
> with 3 parameters.[/color]

That's what std::string is. It's the name of a class.
[color=blue]
> The verbosity of error messages could be reduced to
> a fraction of basic_string, even more when string is used as template
> in other templates.
>[/color]

Okay, that's a legitimate problem. But we're not going to redesign
std::string for that. The real problem is far more extensive: Compiler
writers haven't yet figured out how to give good error messages for
templates. Avoiding templates won't solve this problem. The solution has
to come from compiler writers.

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Abecedarian]

Re: A parameterized class (i.e. template class / class template) is not a class?

Pete Becker wrote:[color=blue]
> Abecedarian wrote:[color=green]
> > The verbosity of error messages could be reduced to
> > a fraction of basic_string, even more when string is used as[/color][/color]
template[color=blue][color=green]
> > in other templates.[/color]
>
> Okay, that's a legitimate problem. But we're not going to redesign
> std::string for that.[/color]

No redesign necessary, just 'translate' basic_string<ch ar, ...> to
class string. Of course, the basic_string template shall remain as it
is. Just the typedef shall be optional with a real string class
(actually 2 classes).
[color=blue]
> The real problem is far more extensive: Compiler
> writers haven't yet figured out how to give good error messages for
> templates.[/color]

They cannot. The problem is situated in the C++ 'template mechanism'.
[color=blue]
> Avoiding templates won't solve this problem.[/color]

Avoiding unnecessary templates for the most frequent use cases really
would mostly solve this problem

A.

[Pete Becker]

Re: A parameterized class (i.e. template class / class template)is not a class?

Abecedarian wrote:[color=blue]
>
> No redesign necessary, just 'translate' basic_string<ch ar, ...> to
> class string. Of course, the basic_string template shall remain as it
> is. Just the typedef shall be optional with a real string class
> (actually 2 classes).
>[/color]

That's just like writing the same function twice: it leads to
maintenance problems and inconsistencies .

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)