[Bug c++/42085] New: Typedef templates

[Bug c++/42085] New: Typedef templates

[marc dot coiffier at free dot fr]

First of all, sorry if I seem redundant, for you may get a lot of requests like
this one, but couldn't you implement an extension (accessible with, for
example, -ftypedef-templates or something) that would allow the code below to
compile as it logically should : 

template<class _T>
typedef _T Storage; // a template typedef declaration

class I { // an abstract class
  virtual void foo() const=0;
};
template<>
typedef const I& Storage<I>; // a partial specialisation for the abstract class

template<class _T>
class Foo {
  Storage<_T> m_data;
/* obviously the class does something else ;) */
};

int main(/* etc. */) {
  Foo<A>   test;
  Foo<int> test2;

  return 0;
}

Thanks a bunch if you can, and thanks anyway otherwise :D

PS: I know the standard doesn't allow for typedef templates (and that's why I'm
asking for an extension) but this one would be so darn helpful I couldn't help
but ask anyway.

PS2: I know there is a workaround to do this, but it's ugly and it's impact on
readability and design is disastrous, whereas the syntax above is pretty
readable and well in accordance with the whole of template declaration and
specialisation, since its syntax is the same as when I declare a class or a
function template.


-- 
           Summary: Typedef templates
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: marc dot coiffier at free dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

[Bug c++/42085] Typedef templates

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2009-11-18 02:10 -------
I think C++0x (well renamed to C++1x) has something like this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

[Bug c++/42085] Typedef templates

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2009-11-18 02:13 -------
(In reply to comment #1)
> I think C++0x (well renamed to C++1x) has something like this.

Called template aliases:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2258.pdf

Note GCC does not implement them yet.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

[Bug c++/42085] Typedef templates

[marc dot coiffier at free dot fr]

------- Comment #3 from marc dot coiffier at free dot fr  2009-11-18 18:13 -------
(In reply to comment #2)
> (In reply to comment #1)
> > I think C++0x (well renamed to C++1x) has something like this.
> 
> Called template aliases:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2258.pdf
> 
> Note GCC does not implement them yet.
> 

Thank you, I looked it up and it does seem to match what I want. Do you know of
any compiler (or compiler branch or compiler extension or plugin), even
experimental, that would let me experience this feature, though ? Also, could
you tell me when they plan to release a stable version of a C++1x compiler ?


-- 

marc dot coiffier at free dot fr changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marc dot coiffier at free
                   |                            |dot fr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

[Bug c++/42085] Typedef templates

[redi at gcc dot gnu dot org]

------- Comment #4 from redi at gcc dot gnu dot org  2009-11-18 18:47 -------
(In reply to comment #3)
> you tell me when they plan to release a stable version of a C++1x compiler ?

After the C++1x standard is finished, which might be next year, or might not. 

I don't know of any compiler that implements template aliases yet. This is the
wrong place to ask, all you'll learn here is GCC doesn't support them


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

[Bug c++/42085] Typedef templates

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42085

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-08-16 10:19:59 UTC ---
I think clang might have implemented template aliases.

Implementing them in G++ is PR 45114

*** This bug has been marked as a duplicate of bug 45114 ***