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[Bug c++/24702] New: Koenig found functoid ref, but "cannot be used as a function"
- From: "pierhyth at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 7 Nov 2005 07:09:06 -0000
- Subject: [Bug c++/24702] New: Koenig found functoid ref, but "cannot be used as a function"
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
The problem relates to functoid objects ("function like" objects, ie
ones with an operator() defined) and references to them within a
namespace. When Koenig lookup is used to find such a
reference-to-functoid, g++ seems to find it okay, but then states
"cannot be used as a function". If I use an actual functoid object
instead of a reference to one, it works fine.
Here is an example:
#include <iostream>
namespace dummyx {
struct Dummy {
Dummy() {}
};
struct DummyFunct {
int operator()(Dummy d) const {return 5;}
static DummyFunct& full() {static DummyFunct f; return f;}
};
static DummyFunct& dummyFunct=DummyFunct::full();
DummyFunct myDummyFunct;
DummyFunct& mymyDummyFunct=myDummyFunct;
}
int main() {
::dummyx::Dummy const d;
std::cout<<"dummyx::dummyFunct(d) = "<<dummyx::dummyFunct(d)<<std::endl;
std::cout<<"dummyFunct(d) = "<<dummyFunct(d)<<std::endl; // fails with 3.4
and 4.0
std::cout<<"myDummyFunct(d) = "<<myDummyFunct(d)<<std::endl;
std::cout<<"mymyDummyFunct(d) = "<<mymyDummyFunct(d)<<std::endl; // fails
with 3.4 and 4.0
}
When I try to compile this code using g++ version 4.0.2 I get the
following errors:
testit.cc: In function ?int main()?:
testit.cc:26: error: ?dummyx::dummyFunct? cannot be used as a function
testit.cc:28: error: ?dummyx::mymyDummyFunct? cannot be used as a function
I see no reason why such references should not be able to be used
as a function. As you see, if it is explicitly namespace-qualified
it can be. And according to Koenig rules, the unqualified name should
indeed be found and, as operator() is applicable for the found reference,
it should be usable as a function. Indeed, this is what version 3.2.3
of g++ does.
The above test code compiles fine with g++ version 3.2.3. The errors
seem only to occur in versions 3.4 and later (certainly they occur for
versions 3.4.5 and 4.0.2.)
Additional version information:
g++ (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-20)
g++-3.4 (GCC) 3.4.5 20050809 (prerelease) (Ubuntu 3.4.4-6ubuntu8)
g++-4.0 (GCC) 4.0.2 20050808 (prerelease) (Ubuntu 4.0.1-4ubuntu9)
--
Summary: Koenig found functoid ref, but "cannot be used as a
function"
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pierhyth at gmail dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24702