On Nov 24, 1998, sbnaran@localhost.localdomain.COM (Siemel Naran) wrote:

> //But is the 'typename' keyword ok to use even if it is not required?

Not always.  From [temp.res]:

5 The  keyword  typename shall only be used in template declarations and
  definitions, [...] The  keyword  typename  shall only be applied to
  qualified names, but those names need not be dependent. [...]

--
Alexandre Oliva  http://www.dcc.unicamp.br/~oliva  aoliva@{acm.org}
oliva@{dcc.unicamp.br,gnu.org,egcs.cygnus.com,samba.org}
Universidade Estadual de Campinas, SP, Brasil


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Siemel Naran wrote:

> #include <vector>

> //We know that typename is required when we have templates.  Eg,

> template <class Container>
> void f(Container const & c)
> {
>      typedef          Container::value_type value_type; // error
>      typedef typename Container::value_type value_type; // ok
> }

> //But is the 'typename' keyword ok to use even if it is not required?

> void g(std::vector<int> const & c)
> {
>      typedef std::vector<int> Container;
>      typedef         Container::value_type value_type; // ok
>      typedef typename Container::value_type value_type; // is this ok?
> }


> Egcs doesn't mind the 'typename' in LINE3 of function g(...)
> It correctly complains about the missing 'typename' in LINE1 of f(...)

> typename.c: In function `void f(const Container &)':
> typename.c:8: `Container::value_type' is not a valid declarator
> typename.c:8:   perhaps you want `typename Container::value_type' to make
>                 it a type
> typename.c:8: parse error before `;'

> */

> /*

> Como doesn't complain about the missing 'typename' in LINE1 of f(...)
> It does complain about the 'typename' in LINE3 of g(...)

> "typename.c", line 19: error: typename may only be used within a template
>        typedef typename Container::value_type value_type; // is this ok?
>                ^

> */

I think both reported errors are real.
According to my reading of 14.6 Name Resolution para.5,
"typename" is only valid within a template, while para.6
REQUIRES the use of "typename" in f().

--

Chris Kuan, BHP Information Technology
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"A Design Pattern is something that got left out of the language"
- Richard O'Keefe



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#include <vector>

//We know that typename is required when we have templates.  Eg,

template <class Container>
void f(Container const & c)
{
     typedef          Container::value_type value_type; // error
     typedef typename Container::value_type value_type; // ok
}


//But is the 'typename' keyword ok to use even if it is not required?

void g(std::vector<int> const & c)
{
     typedef std::vector<int> Container;
     typedef         Container::value_type value_type; // ok
     typedef typename Container::value_type value_type; // is this ok?
}


//I'm changing my code from a template to a non-template, and I'm lazy
//to take the typename out :).  Besides, the 'typename' looks nice
//there as a comment.  And it has a cool color on my editor.

int main()
{
     f(std::vector<double>());
}


/*

Egcs doesn't mind the 'typename' in LINE3 of function g(...)
It correctly complains about the missing 'typename' in LINE1 of f(...)

typename.c: In function `void f(const Container &)':
typename.c:8: `Container::value_type' is not a valid declarator
typename.c:8:   perhaps you want `typename Container::value_type' to make
                it a type
typename.c:8: parse error before `;'

*/

/*

Como doesn't complain about the missing 'typename' in LINE1 of f(...)
It does complain about the 'typename' in LINE3 of g(...)

"typename.c", line 19: error: typename may only be used within a template
       typedef typename Container::value_type value_type; // is this ok?
               ^

*/

So who is right?  To me, it seems like egcs is right on both counts.

--
----------------------------------
Siemel B. Naran (sbnaran@uiuc.edu)
----------------------------------


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