| Summary: | Unrecognizing static function as a template parameter when its return value is also templated | ||
|---|---|---|---|
| Product: | gcc | Reporter: | SATo <sato> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | gcc-bugs, reichelt |
| Priority: | P2 | Keywords: | monitored, rejects-valid |
| Version: | 3.3.1 | ||
| Target Milestone: | 3.4.3 | ||
| Host: | Target: | ||
| Build: | Known to work: | 3.4.3 4.0.0 | |
| Known to fail: | 2.95.3 3.2.3 3.3.3 3.4.0 | Last reconfirmed: | 2004-09-09 03:57:03 |
Confirmed. Confirmed indeed. This never worked, and still doesn't.
One rather confusing thing: for this code snippet
-------------
template <int (*)()> class Far {};
struct Boo {
static int some();
typedef Far<some> far_type;
};
-------------
we get
g/x> /home/bangerth/bin/gcc-3.5-pre/bin/c++ -c x.cc
x.cc:4: error: `static int Boo::some()' cannot appear in a constant-expression
x.cc:4: error: template argument 1 is invalid
x.cc:4: error: ISO C++ forbids declaration of `far_type' with no type
(which I find particularly confusing because the error message refers to
Boo::some -- which I didn't write this way, and as the submitter correctly
noticed: had I written it in this way, the compiler had accepted it.
However, it gets worse: if I don't use the automatic decay to a function
pointer and write the address-of explicitly, i.e.
------------------
template <int (*)()> class Far {};
struct Boo {
static int some();
typedef Far<&some> far_type;
};
------------------
then the error message changes to the even more unreadable
g/x> /home/bangerth/bin/gcc-3.5-pre/bin/c++ -c x.cc
x.cc:4: error: missing `>' to terminate the template argument list
x.cc:4: error: template argument 1 is invalid
x.cc:4: error: ISO C++ forbids declaration of `some' with no type
x.cc:4: error: expected `;' before '>' token
Which is totally bogus.
W.
Fixed by Mark's patch for PR 17585: http://gcc.gnu.org/ml/gcc-cvs/2004-09/msg01289.html |
avr-gcc.EXE (GCC) 3.3.1 Reading specs from C:\WinAVR\bin\..\lib\gcc-lib\avr\3.3.1\specs Configured with: ../configure --prefix=/e/avrdev/install --target=avr --enable- languages=c,c++ --disable-nls --enable-win32-registry=WinAVR Thread model: single gcc version 3.3.1 mingw32-gcc.EXE (GCC) 3.2 (mingw special 20020817-1) Reading specs from c:/mingw/bin/../lib/gcc-lib/mingw32/3.2/specs Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as -- host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls -- enable-languages=f77,c++,objc,ada --disable-win32-registry --disable-shared Thread model: win32 gcc version 3.2 (mingw special 20020817-1) > avr-gcc test.cpp test.cpp:10: error: invalid use of undefined type `class Boo' test.cpp:6: error: forward declaration of `class Boo' test.cpp:10: error: template argument 2 is invalid test.cpp:10: error: ISO C++ forbids declaration of `far_type' with no type test.cpp: ------------------------- template <class Val, Val func()> class Far {}; class Boo { public: static int some(); typedef Far<int, some> far_type; // error }; int main() { } ---------------------------------- BUT this file will be compiled successfully test.cpp: ------------------------- template <class Val, Val func()> class Far {}; class Boo { public: static int some(); typedef Far<int, Boo::some> far_type; // ok (explicit scope specifier) }; int main() { } ----------------------------------