[Bug c++/57063] Valid static_cast from data member to rvalue reference fails to compile
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57063
--- Comment #2 from Nikolka tsoae at mail dot ru 2013-04-25 07:19:20 UTC ---
The alias is added for convenience - we can quickly test handling of different
types so. It seems that there is no problem with class types and function
types, the error arises when T is a scalar type or an array type:
#include string
template class T
struct X
{
T f()
{
return static_castT (value);
}
T value;
};
enum E {};
template class Xint;
template class XE;
template class Xstd::string;
template class Xint();
template class Xint[1];
test.cpp: In instantiation of ‘T XT::f() [with T = int]’:
test.cpp:15:20: required from here
test.cpp:8:43: error: cannot bind ‘int’ lvalue to ‘int’
return static_castT (value);
^
test.cpp: In instantiation of ‘T XT::f() [with T = E]’:
test.cpp:16:20: required from here
test.cpp:8:43: error: cannot bind ‘E’ lvalue to ‘E’
test.cpp: In instantiation of ‘T XT::f() [with T = int [1]]’:
test.cpp:19:20: required from here
test.cpp:8:43: error: cannot bind ‘int [1]’ lvalue to ‘int ()[1]’
[Bug c++/57063] Valid static_cast from data member to rvalue reference fails to compile
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57063 --- Comment #3 from Paolo Carlini paolo.carlini at oracle dot com 2013-04-25 08:34:30 UTC --- In general, testcases must be minimal, otherwise, eg, you start wondering (as I did) whether the bug is in the code handling alias declarations.
[Bug c++/57063] Valid static_cast from data member to rvalue reference fails to compile
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57063
--- Comment #4 from Nikolka tsoae at mail dot ru 2013-04-25 13:51:21 UTC ---
It looks like the root of the issue is that static_cast produces an expression
with wrong value category sometimes.
#include iostream
#include type_traits
#define PRINT_VALUE(...) \
std::cout #__VA_ARGS__ = __VA_ARGS__ std::endl
template class T
struct X
{
void f()
{
PRINT_VALUE(std::is_lvalue_reference
decltype(static_castT (value)){});
PRINT_VALUE(std::is_rvalue_reference
decltype(static_castT (value)){});
std::cout std::endl;
}
T value;
};
struct A {};
int main()
{
Xint{0}.f();
XA{A()}.f();
}
When T = int, static_castT (value) is wrongfully treated as an lvalue. In
the first example the compiler thinks that we want to return lvalue of type int
by rvalue reference int , which would be invalid.
[Bug c++/57063] Valid static_cast from data member to rvalue reference fails to compile
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57063
Paolo Carlini paolo.carlini at oracle dot com changed:
What|Removed |Added
Status|UNCONFIRMED |NEW
Last reconfirmed||2013-04-24
Ever Confirmed|0 |1
--- Comment #1 from Paolo Carlini paolo.carlini at oracle dot com 2013-04-24
21:44:16 UTC ---
The alias declaration doesn't play a role:
struct X
{
int f()
{
return static_castint(value);
}
int value;
};
