class vs. typename

[Alexander Malkis]

What's the semantical/syntactical difference between two keywords
"class" and "typename" (apart from different spelling)?

--
Best regards,
Alex.

PS. To email me, remove "loeschedie s" from the email address given.

[John Harrison]

Re: class vs. typename


"Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in message
news:c4uupa$cbc $1@hades.rz.uni-saarland.de...[color=blue]
> What's the semantical/syntactical difference between two keywords
> "class" and "typename" (apart from different spelling)?
>[/color]

None at all.

I think typename was introduced because not all template parameters are
classes.

john

[John Harrison]

Re: class vs. typename


"Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in message
news:c4uupa$cbc $1@hades.rz.uni-saarland.de...[color=blue]
> What's the semantical/syntactical difference between two keywords
> "class" and "typename" (apart from different spelling)?
>[/color]

None at all.

I think typename was introduced because not all template parameters are
classes.

john

[Steven T. Hatton]

Re: class vs. typename

John Harrison wrote:
[color=blue]
>
> "Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in
> message news:c4uupa$cbc $1@hades.rz.uni-saarland.de...[color=green]
>> What's the semantical/syntactical difference between two keywords
>> "class" and "typename" (apart from different spelling)?
>>[/color]
>
> None at all.
>
> I think typename was introduced because not all template parameters are
> classes.
>
> john[/color]
I believe we need to restrict the discussion to template parameters in order
for that to hold. This is from the C++ Standard:

"There is no semantic difference between class and typename in a
template-parameter."

Just being pedantic.
--
p->m == (*p).m == p[0].m

http://www.kdevelop.org

http://www.suse.com

http://www.mozilla.org

[Steven T. Hatton]

Re: class vs. typename

John Harrison wrote:
[color=blue]
>
> "Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in
> message news:c4uupa$cbc $1@hades.rz.uni-saarland.de...[color=green]
>> What's the semantical/syntactical difference between two keywords
>> "class" and "typename" (apart from different spelling)?
>>[/color]
>
> None at all.
>
> I think typename was introduced because not all template parameters are
> classes.
>
> john[/color]
I believe we need to restrict the discussion to template parameters in order
for that to hold. This is from the C++ Standard:

"There is no semantic difference between class and typename in a
template-parameter."

Just being pedantic.
--
p->m == (*p).m == p[0].m

http://www.kdevelop.org

http://www.suse.com

http://www.mozilla.org

[Leor Zolman]

Re: class vs. typename

On Tue, 6 Apr 2004 20:45:09 +0100, "John Harrison"
<john_andronicu s@hotmail.com> wrote:
[color=blue]
>
>"Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in message
>news:c4uupa$cb c$1@hades.rz.un i-saarland.de...[color=green]
>> What's the semantical/syntactical difference between two keywords
>> "class" and "typename" (apart from different spelling)?
>>[/color]
>
>None at all.
>
>I think typename was introduced because not all template parameters are
>classes.[/color]
Actually it was introduced in order to inform the compiler that a name
dependent upon a template parameter is a type; Standard C++ assumes that it
is not in that context unless the typename keyword is used. However, many
existing implementations allow the "typename" to be omitted in that
context, some [like gcc] at least warning you about the assumptions being
made.

I think they chose to allow "typename" instead of "class" for template
parameters after the fact, simply as a way to document the nature of the
type parameters expected. This is one of stylistic issues for which the
"pendulum" still seems to be swinging...
-leor
[color=blue]
>
>john
>[/color]

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

Re: class vs. typename

On Tue, 6 Apr 2004 20:45:09 +0100, "John Harrison"
<john_andronicu s@hotmail.com> wrote:
[color=blue]
>
>"Alexander Malkis" <alexloeschedie smalk@stone.cs. uni-sb.de> wrote in message
>news:c4uupa$cb c$1@hades.rz.un i-saarland.de...[color=green]
>> What's the semantical/syntactical difference between two keywords
>> "class" and "typename" (apart from different spelling)?
>>[/color]
>
>None at all.
>
>I think typename was introduced because not all template parameters are
>classes.[/color]
Actually it was introduced in order to inform the compiler that a name
dependent upon a template parameter is a type; Standard C++ assumes that it
is not in that context unless the typename keyword is used. However, many
existing implementations allow the "typename" to be omitted in that
context, some [like gcc] at least warning you about the assumptions being
made.

I think they chose to allow "typename" instead of "class" for template
parameters after the fact, simply as a way to document the nature of the
type parameters expected. This is one of stylistic issues for which the
"pendulum" still seems to be swinging...
-leor
[color=blue]
>
>john
>[/color]

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:

https://www.bdsoft.com/tools/stlfilt.html

[Asfand Yar Qazi]

Re: class vs. typename

Alexander Malkis wrote:[color=blue]
> What's the semantical/syntactical difference between two keywords
> "class" and "typename" (apart from different spelling)?
>[/color]

"class" has less characters in it than "typename", so saves more trees.

:-)


--

http://www.it-is-truth.org/

[Asfand Yar Qazi]

Re: class vs. typename

Alexander Malkis wrote:[color=blue]
> What's the semantical/syntactical difference between two keywords
> "class" and "typename" (apart from different spelling)?
>[/color]

"class" has less characters in it than "typename", so saves more trees.

:-)


--

http://www.it-is-truth.org/

[Steven T. Hatton]

Re: class vs. typename

Alexander Malkis wrote:
[color=blue]
> What's the semantical/syntactical difference between two keywords
> "class" and "typename" (apart from different spelling)?
>[/color]
I don't know if anybody mentioned this, I just learned it. It is discussed
in TC++PL(SE) Appendix C.13.5. Stroustrup explains it as a way of
disambiguating statements in template declarations. For example


template<class C> void h(C& v)
{
typename C::iterator i = v.begin();
}

--
STH
Hatton's Law: "There is only One inviolable Law"
KDevelop: http://www.kdevelop.org SuSE: http://www.suse.com
Mozilla: http://www.mozilla.org

[NPC]

Re: class vs. typename


"Steven T. Hatton" <susudata@setid ava.kushan.aa> wrote in message
news:MpKdnaADE6 a_NOTdRVn-jA@speakeasy.ne t...[color=blue]
> Alexander Malkis wrote:
>[color=green]
> > What's the semantical/syntactical difference between two keywords
> > "class" and "typename" (apart from different spelling)?
> >[/color]
> I don't know if anybody mentioned this, I just learned it. It is[/color]
discussed[color=blue]
> in TC++PL(SE) Appendix C.13.5. Stroustrup explains it as a way of
> disambiguating statements in template declarations. For example
>
>
> template<class C> void h(C& v)
> {
> typename C::iterator i = v.begin();
> }
>
> --
> STH
> Hatton's Law: "There is only One inviolable Law"
> KDevelop: http://www.kdevelop.org SuSE: http://www.suse.com
> Mozilla: http://www.mozilla.org[/color]


Sometimes compilers need some guidance. Typename is a way of telling the
compiler that C::iterator is a C++ Type (as opposed to a C++ function call,
for example).
You will only see typename used in contexts related to programs using
templates.
As far as how/when to use typename : use it when inside of a templated
class/function and refering to a typedef belonging to the templated
parameter. For example, C in you code above is a templated parameter.
iterator is a typedef defined in C. Therefore, you must use the typename
keyword when declaring an object of that type (or if re-typedef'ing (in C):
typedef typename C::iterator IteratorType).

NPC