https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96746
Bug ID: 96746
Summary: Type Casting in template function should not be
type-dependent if the type of the conversion result is
not type-dependent.
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: masamitsu.murase at gmail dot com
Target Milestone: ---
The following code compiles fine with GCC 11.0, but I think that it should not
compile
because of the mismatch of the argument type of "func_with_int_arg" at (*1) .
#include <type_traits>
void func_with_int_arg(int) {}
template<typename T>
std::enable_if_t<std::is_same<T, int*>::value>
func(T arg)
{
func_with_int_arg(static_cast<int*>(arg)); // (*1)
}
template<typename T>
std::enable_if_t<std::is_same<T, int>::value>
func(T) {}
int main(int, char **)
{
func(1); // Instantiate func<int>
}
According to C++17 specification, "static_cast<int*>(arg)" is NOT
type-dependent.
because "int*" is not dependent.
"17.6.2.2 Type-dependent expressions" says as follows:
Expressions of the following forms are type-dependent only if the type
specified by the type-id, simple-type-specifier or new-type-id is
dependent,
even if any subexpression is type-dependent:
...(snip)...
dynamic_cast <type-id> (expression)
static_cast <type-id> (expression)
const_cast <type-id> (expression)
...(snip)...
Therefore, "func_with_int_arg(static_cast<int*>(arg));" at (*1) should cause a
hard error
instead of a substitution failure.
By the way, the above code does not compile fine with Clang 12.0.
The error message is:
sample.cpp:9:9: error: no matching function for call to 'func_with_int_arg'
func_with_int_arg(static_cast<int*>(arg)); // (*1)
^~~~~~~~~~~~~~~~~
sample.cpp:3:10: note: candidate function not viable: no known conversion
from 'int *' to 'int' for 1st argument; dereference the argument with *
void func_with_int_arg(int) {}
^
1 error generated.
Regards,
Murase
