[Bug c++/40944] New: [C++0x] rejects well-formed code: SFINAE, decltype, function call

[Bug c++/40944] New: [C++0x] rejects well-formed code: SFINAE, decltype, function call

[s dot gesemann at gmail dot com]

I think the following code is well-formed and should compile with the
-std=c++0x switch:

   #include <iostream>

   template<typename T>
   struct make { static T&& it(); };

   template<typename R, typename... T>
   struct exists { typedef R type; };

   template< typename Func, typename T >
   void bar(T const& x,
     typename exists<
       int,
       decltype( make<Func>::it()(make<T const&>::it()) ) // SFINAE!
     >::type = 0
   ) {
     std::cout << "bar-1\n";
   }

   template< typename Func >
   void bar(...) {
     std::cout << "bar-2\n";
   }

   int main() {
     bar<void(*)(int&)>(42);
   }

I expect it to compile and print "bar-2". Instead, the compiler rejects the
code with the error

   invalid initialization of reference >int&< with an expression of
   type >const int<.

Cheers!
SG


-- 
           Summary: [C++0x] rejects well-formed code: SFINAE, decltype,
                    function call
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: s dot gesemann at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[jwakely dot gcc at gmail dot com]

------- Comment #1 from jwakely dot gcc at gmail dot com  2009-08-04 12:35 -------
I think you're right that this is a bug, this is a slightly reduced testcase
showing the same error:

template<typename T>
struct make { static T&& it(); };

void (*pf)(int&) = 0;

template< typename T >
int bar(T const& x,
        decltype( pf(make<T const&>::it()) )* = 0 // SFINAE!
        ) {
    return 1;
}

int bar(...) {
    return 0;
}

int main() {
    return bar(42);
}

I think this should compile and return 0


-- 

jwakely dot gcc at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jwakely dot gcc at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[s dot gesemann at gmail dot com]

------- Comment #2 from s dot gesemann at gmail dot com  2009-08-16 12:48 -------
This is probably a related (SFINAE<->decltype) problem:


template<typename T>
struct meta {
   static T&& m();   // make
   static void s(T); // sink
};

// operator()(T&,int) available ?
template<typename T, typename = decltype( meta<T&>::m()(23) )>
int foo(T x) {
   x(23);
   return 1;
}

int foo(...) {
   return 0;
}

int main() {
   return foo(42);
}


As far as I can tell it should compile with -std=c++0x and return 0. Instead,
the compiler rejects the code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[s dot gesemann at gmail dot com]

------- Comment #3 from s dot gesemann at gmail dot com  2009-08-16 13:00 -------
sorry, please disregard my previous comment. I accidentally used GCC 4.3.3
instead of GCC 4.4.1


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[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         |2009-11-03 16:21:06
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[jason at gcc dot gnu dot org]

------- Comment #4 from jason at gcc dot gnu dot org  2009-11-03 17:11 -------
Subject: Bug 40944

Author: jason
Date: Tue Nov  3 17:11:18 2009
New Revision: 153856

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153856
Log:
        PR c++/40944
        * call.c (initialize_reference): Add complain parm.
        * typeck.c (convert_for_initialization): Pass it.
        * decl.c (grok_reference_init): Likewise.
        * cp-tree.h: Declare it.

Added:
    trunk/gcc/testsuite/g++.dg/template/sfinae15.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944

[Bug c++/40944] [C++0x] rejects well-formed code: SFINAE, decltype, function call

[jason at gcc dot gnu dot org]

------- Comment #5 from jason at gcc dot gnu dot org  2009-11-03 18:49 -------
Fixed for 4.5.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40944