Template template parameters

Hello,

Does anyone know why this declaration compiles:

template< template<typenameclass T>
class X { /*...*/ };

while this one doesn't:

template< template<typenametypename T>
class X { /*...*/ };


I thought "class" and "typename" were equivalent in template
declarations?

I don't think it's my compiler's fault (VC8) because I couldn't find
references to syntaxes like the second one on the web, only like the
first one, so there must be a logical reason...

Even Comeau's FAQ uses the first form, without even mentioning the
second one.

Thanks by advance.

--
IR

re: Template template parameters

IR wrote:They are, but only if you use them alone. What you have here is
a template template argument and you cannot use 'typename' there,
it has to be 'class'. See 14.1/1 for the syntax.
Because there is no "second one". The syntax rules require "class"
there.

V
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re: Template template parameters

Victor Bazarov wrote:
[...][...]

Thanks for the answer Victor.
From now on I'll try to look _also_ in the standard before posting
stupid questions on a newsgroup... ;-)

Cheers.
--
IR

re: Template template parameters

In article <Xns9866E3133FB7EZjx3HdoP0Qwt@194.177.96.26>,
IR <no_email@use.netwrote:If I understand you, there is no second one. See revision at:

http://www.comeaucomputing.com/techtalk/#typename
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Greg Comeau / 20 years of Comeauity! Intel Mac Port now in beta!
Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
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re: Template template parameters

IR wrote:No, they are not. In some places they are eqivalent, in others they
are not. You found one of those!

The opposite example is

template<class T, typename T::some_type>
stuct X;

Here, the class keyword can be replaces by typename, but the typename
in the second parameter cannot be replaced by class.

So, using typename in place of class can be confusing!


Bo Persson

re: Template template parameters

Greg Comeau wrote:

[snip]I was rather refering to the template template section :
http://www.comeaucomputing.com/techtalk/templates/#ttp

which clearly uses

template <template <typename Tclass Product>...

whereas it uses typename everywhere else.

--
IR

re: Template template parameters

Bo Persson wrote:
[snip]Isn't this very example a (non-)dependent name lookup disambiguation?
(or whatever it is called... I guess you get the point anyway :p)

--
IR

re: Template template parameters

In article <Xns9867E986373FCZjx3HdoP0Qwt@194.177.96.26>,
IR <no_email@use.netwrote:Then see http://www.comeaucomputing.com/techt...ates/#typename :)
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in beta!
Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

re: Template template parameters

Greg Comeau wrote:

....Oops my bad, I didn't see it yesterday. :)

--
IR