http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617
Summary: [C++0x] Problem with non-type template parameters and
decltype
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: [email protected]
ReportedBy: [email protected]
gcc 4.7.0 in C++0x mode rejects the following program:
//---------------
template<class T, decltype(T())> // #
struct A {};
A<int, 0> a;
int main() {}
//---------------
The error message annotated at line # is:
"error: 'decltype (T())' is not a valid type for a template constant parameter"
It seems to me that according to the FDIS this should be well-formed program:
decltype is feasible as a /parameter-declaration/. The new type-equivalence
rules in [temp.type] p. 2,
"If an expression e involves a template parameter, decltype(e) denotes a unique
dependent type. Two such decltype-specifiers refer to the same type only if
their expressions are equivalent (14.5.6.1)."
should allow for a compiler to deduce the meaning similar to other dependent
contexts. See also [temp.dep.type] p. 8 for this matter:
"A type is dependent if it is [...] denoted by decltype(expression), where
expression is type-dependent (14.6.2.2)."
