Is it possible to typedef a template class? How?

For example:

template <class T>
class OldClass
{
};

typedef OldClass<T> NewClass<T>;

void main()
{
NewClass<int> o;
}

Thanks!

"pradosh" <pradosh.sivadoss@gmail.com> wrote in message
news:1125512660.302522.68100@z14g2000cwz.googlegro ups.com...[color=blue]
> Is it possible to typedef a template class? How?[/color]

You must typedef a particular instantiation. See below.
[color=blue]
>
> For example:
>
> template <class T>
> class OldClass
> {
> };
>
> typedef OldClass<T> NewClass<T>;[/color]

typedef OldClass<int> NewClass;
[color=blue]
>
> void main()[/color]

int main()
[color=blue]
> {
> NewClass<int> o;[/color]

NewClass o;
[color=blue]
> }
>
> Thanks![/color]

-Mike

pradosh wrote:[color=blue]
> Is it possible to typedef a template class?[/color]

Technically speaking, there is no such thing as "a template class", so,
no, there is no way to typedef it. Now, if you mean "a class template",
then the answer is "yes, kinda, but not really".
[color=blue]
> How?
>
> For example:
>
> template <class T>
> class OldClass
> {
> };
>
> typedef OldClass<T> NewClass<T>;
>
> void main()[/color]

int main()
[color=blue]
> {
> NewClass<int> o;
> }[/color]

There are no template typedefs yet in the language (there is a proposal
about them, though), so you need to do a small trick to achieve what you
need:

template<class T> class OldClass {};

template<class T> struct NewClass { typedef OldClass<T>::type; };

int main()
{
NewClass<int>::type o; // same as 'OldClass<int> o;'
}

And it probably covered in the FAQ. Please take a read of the FAQ. You
can find it here: http://www.parashift.com/c++-faq-lite/

V

In article <1125512660.302522.68100@z14g2000cwz.googlegroups. com>,
"pradosh" <pradosh.sivadoss@gmail.com> wrote:
[color=blue]
> Is it possible to typedef a template class? How?
>
> For example:
>
> template <class T>
> class OldClass
> {
> };
>
> typedef OldClass<T> NewClass<T>;
>
> void main()
> {
> NewClass<int> o;
> }
>
> Thanks![/color]

Sort of, not really. You can do this:

template <class T>
class OldClass
{
};

template <class T>
struct NewClass
{
typedef OldClass<T> type;
};

int main()
{
NewClass<int>::type o;
}

There is a proposal before the committee that would allow the following:

template <class T>
class OldClass
{
};

template <class T>
using NewClass = OldClass<T>;

int main()
{
NewClass<int> o;
}

To the best of my knowledge this one has general support on the
committee and the authors are working on proposed wording.

-Howard

"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message
news:J0nRe.31451$Tf5.25546@newsread1.mlpsca01.us.t o.verio.net...[color=blue]
> pradosh wrote:[color=green]
>> Is it possible to typedef a template class?[/color]
>
> Technically speaking, there is no such thing as "a template class",[/color]

It is obvious that the original poster meant "class template"; but
confusingly, the term "template class" exists as well.

It's sometimes used in place of "class template," but sometimes used to mean
an instance of a class template. David Vandevoorde and Nicolai Josuttis
accept this usage, explain the situation in Chapter 7 of their book C++
Templates, and avoid to use the term :)

If we accept "template class" to mean an instance of a class, then the
answer to the original question is trivial:

typedef OldClass<int> NewClass;

But OP didn't ask that :)

Ali