[Bug c++/50586] New: Template argument of type "pointer to function" of a template class causes usage error if template is instantiated with pointer-to-private-static-member-function
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50586
Bug #: 50586
Summary: Template argument of type "pointer to function" of a
template class causes usage error if template is
instantiated with
pointer-to-private-static-member-function
Classification: Unclassified
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: mouchta...@gmail.com
Created attachment 25390
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25390
A small test file exhibiting the error.
If there is a declared template class, which accepts a pointer-to-function as a
non-type template parameter:
//
template
struct caller
{ int operator () (void) const { return (*f)(); } };
//
and is instantiated in a class with a pointer to a private static member
function:
//
class A {
static int f (void) { return 0; }
public:
caller<&f> get;
};
//
then G++ reports that "f" is private when used in the context of
caller::operator().
I haven't found anything in the standard that would impose this restriction.
(As a cue, this was reported as an error as well in older version of the vc
compiler, but in version 16.00 it is not an error any more)
I am attaching a small test file. I am not attaching any preprocessed file, as
there is no need. No preprocessor directives are used in this test.
I hope this has not been dealt before.
- Detailed information ---
*** Compiler version: ***
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/spare/root/libexec/gcc/i686-pc-linux-gnu/4.6.1/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../gcc-4.6.1/configure --prefix=/spare/root
Thread model: posix
gcc version 4.6.1 (GCC)
*** Compilation command: ***
g++ -ansi -pedantic -Wall -Wextra t.cpp
*** Compiler output: ***
t.cpp: In member function 'int caller::operator()() const [with int (* f)()
= A::f]':
t.cpp:26: instantiated from here
t.cpp:13: error: 'static int A::f()' is private
t.cpp:5: error: within this context
[Bug libstdc++/65013] New: [API] std::deque is missing constructors
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65013 Bug ID: 65013 Summary: [API] std::deque is missing constructors Product: gcc Version: 4.9.2 Status: UNCONFIRMED Severity: minor Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: mouchtaris at gmail dot com std::deque (at least) is missing constructors for copy/move-constructing with a different allocator. deque( const deque& other, const Allocator& alloc ); deque( deque&& other, const Allocator& alloc ); (Reminding-mention: the first of these needs to use std::allocator_traits::select_on_container_copy_construction(alloc) in case no allocator is provided).
[Bug c++/63924] New: Constexpr constructible expression "is not constexpr" when used in a template non-type argument
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63924
Bug ID: 63924
Summary: Constexpr constructible expression "is not constexpr"
when used in a template non-type argument
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mouchtaris at gmail dot com
A proper constexpr constructible type is found non-constexpr by the compiler,
under the following conditions:
- it is used in an expression which is passed as a template non-type argument,
- its copy constructor is defaulted (whether explicitly or implicitly).
In the following test case this is demostrated:
// ---
// File t.cpp
// ---
// utils
template struct require_constexpr {
static constexpr unsigned value = N;
};
template constexpr void noop (void) { }
// a constexpr constructible class
struct test {
constexpr unsigned size() const { return 0; }
constexpr test() { }
constexpr test(const test &) = default;
};
// size wrappers
constexpr auto size0 (test t) { return t.size(); }
// just making sure type "test" is still considered
constexpr auto size1 (test t) { return size0(t); }
// constexpr constructible outside a template argument
constexpr auto size2 (test t) { return size1(t); }
// PROBLEM here
constexpr auto size3 (test t) { return require_constexpr< size0(t) >::value; }
int main (int, char**)
{
constexpr auto const ar = test { };
noop<
require_constexpr< size3(ar) >
>();
return 0;
}
// ---
Compiling with
g++ -std=c++1y -pedantic -Wall -Wextra -o /tmp/a t.cpp
and here is the output:
//
t.cpp: In function ‘constexpr auto size3(test)’:
t.cpp:22:68: error: ‘t’ is not a constant expression
constexpr auto size3 (test t) { return require_constexpr< size0(t) >::value; }
^
t.cpp:22:68: note: in template argument for type ‘unsigned int’
t.cpp:22:16: error: invalid return type ‘void’ of constexpr function ‘constexpr
auto size3(test)’
constexpr auto size3 (test t) { return require_constexpr< size0(t) >::value; }
^
t.cpp: In function ‘int main(int, char**)’:
t.cpp:29:34: error: could not convert template argument ‘size3((ar, test()))’
to ‘unsigned int’
require_constexpr< size3(ar) >
^
t.cpp:30:5: error: no matching function for call to ‘noop()’
>();
^
t.cpp:30:5: note: candidate is:
t.cpp:6:39: note: template constexpr void noop()
template constexpr void noop (void) { }
^
t.cpp:6:39: note: template argument deduction/substitution failed:
t.cpp:30:5: error: template argument 1 is invalid
>();
^
//
"test" is still properly constexpr-copy-constructed when used outside
template arguments, as in size1() and size2().
The code segment also compiles cleanly if we define a non-default constructor.
In other words, if we change line
constexpr test(const test &) = default;
to
constexpr test(const test &) { }
So the bug (probably) pertrains to defaulting constructors and the use of such
in non-type template arguments.
[Bug c++/63924] Constexpr constructible expression "is not constexpr" when used in a template non-type argument
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63924 --- Comment #1 from Nikos --- Special thanks and kudos to "T.C." for helping figuring this out: http://stackoverflow.com/questions/25465379
[Bug c++/63924] Constexpr constructible expression "is not constexpr" when used in a template non-type argument
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63924 --- Comment #5 from Nikos --- I am sorry, it is missing from the original test case, but noop< require_costexpr< size0(ar) >, require_constexp< size1(ar) > >(); compiles fine. If the issue about test's trivial byte-wise copy construction is true, shouldn't it cause the degenaration of size0's and size1's constexpr-ness and cause errors in their usage as template arguments? Standard-addressing issues are mentioned in the stackoverflow link I have provided. Specifically, the following comes from §12.8 [class.copy]/p13: If the implicitly-defined constructor would satisfy the requirements of a constexpr constructor (7.1.5), the implicitly-defined constructor is constexpr. I don't see why an implicit constructor copying a literal padding byte is not a constexpr constructor. The compiler, I assume, is capable of keeping track of padding bytes as literals at compile time. Or am I mistaken? Thanks a lot for the fix, and thanks a lot for such a quick response.
