[Bug c++/40315] template instantiation fails when using const typename

[Bug c++/40315] template instantiation fails when using const typename

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-04 17:38:37 UTC ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_closed.html#1001 is NAD so I
think we can close this bug as INVALID

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|SUSPENDED                   |RESOLVED
         Resolution|                            |INVALID

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-04 18:14:36 UTC ---
Agreed.

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
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             Status|NEW                         |SUSPENDED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
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                 CC|                            |jason at gcc dot gnu dot org
         AssignedTo|jason at gcc dot gnu dot org|unassigned at gcc dot gnu
                   |                            |dot org
             Status|SUSPENDED                   |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

------- Comment #9 from jason at gcc dot gnu dot org  2010-02-19 21:21 -------
Suspending until the committee can rule on this, but I expect the result to be
that the testcase is ill-formed.


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jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
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             Status|ASSIGNED                    |SUSPENDED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[paolo dot carlini at oracle dot com]

------- Comment #8 from paolo dot carlini at oracle dot com  2009-11-08 23:41 -------
Jason, the extra const in the library code is definitely unintended, I'm going
to remove it anyway.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

------- Comment #7 from jason at gcc dot gnu dot org  2009-11-08 23:32 -------
Created an attachment (id=18996)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18996&action=view)
patch

Here's a patch that fixes the testcase and passes regression testing, but I
don't think it's the right way to go.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

------- Comment #6 from jason at gcc dot gnu dot org  2009-11-08 23:06 -------
Actually, I'm not so sure:

template<class T>
struct A
{
  typedef A arr[3];
};

template<class T>
void f(const typename A<T>::arr) { }

template void f<int>(const A<int>::arr); // #1

template <class T>
struct B
{
  void g(T);
};

template <class T>
void B<T>::g(const T) { } // #2 

it seems to me that either #1 is well-formed, or #2 is, though it might make
sense to recompute the function type from the parameter type...in any case, I'm
opening a DR about this.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

------- Comment #5 from jason at gcc dot gnu dot org  2009-11-08 04:37 -------
I think this is a bug; we shouldn't be dropping the const at template parsing
time.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[jason at gcc dot gnu dot org]

-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jason at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-11-08 04:33:37
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[doriankrause at web dot de]

------- Comment #4 from doriankrause at web dot de  2009-08-26 19:26 -------
Thanks Jonathan for your explanation. Now I can understand the reason behind
this... (though I'm not really happy with the fact that you need to understand
sort of internals to see why code doesn't compile). 

Do I need to mark the bug-report as invalid, or how does it work?

Thanks!


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[redi at gcc dot gnu dot org]

------- Comment #3 from redi at gcc dot gnu dot org  2009-08-26 14:51 -------
(In reply to comment #2)
> IIUC, the top-level const qualifier on "const typename Foo<D>::double3" in the
> primary template applies to the type, which is not known during phase 1

i.e. it's equivalent to "typename Foo<D>::double3 const" which is equivalent to
simply "typename Foo<D>::double3) because top-level cv-qualifiers are removed
from function parameters.

but when double3 is known to be an array type, which is replaced by a pointer
in a parameter list, then the declaration's meaning changes.

Consider:

typedef double  double3[3];
void f(const double3);
typedef void (*ptr)(const double*);
ptr p = f;

This demonstrates that the declaration of 'f' is equivalent to:

void f(const double*);

not

void f(double* const);

According to [dcl.fct] array parameters are replaced with pointers before
top-level cv-qualifiers are deleted.

I think GCC is correct, the template specializations are invalid.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[redi at gcc dot gnu dot org]

------- Comment #2 from redi at gcc dot gnu dot org  2009-08-26 14:43 -------
IIUC, the top-level const qualifier on "const typename Foo<D>::double3" in the
primary template applies to the type, which is not known during phase 1

At instantiation time, double3 is known to be an array type, so decays to a
pointer, and the parameter type becomes "const double*" _not_ "double* const"

So the explicit instantiation creates a type which does not match the primary
template, so it cannot be a specialisation of it.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315

[Bug c++/40315] template instantiation fails when using const typename

[bangerth at gmail dot com]

------- Comment #1 from bangerth at gmail dot com  2009-08-25 15:39 -------
Hm, interesting. I would have thought as well that the code should compile.
On the other hand, icc also produces the same error message, so I am now
officially confused...


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bangerth at gmail dot com changed:

           What    |Removed                     |Added
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                 CC|                            |bangerth at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40315