https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67437
Bug ID: 67437
Summary: [5/6 Regression] Template can't use const value of
explicitly instantiated instance in a const expression
Product: gcc
Version: 5.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Bernhard.Rosenkranzer at linaro dot org
Target Milestone: ---
The following code builds fine with gcc versions up to 4.9 and with any version
of clang, but fails with gcc 5.1, 5.2 and trunk:
template <int N>
struct I0ATerm {
static const double value = I0ATerm<N-1>::value * (2.*N-1.) * (2.*N-1.)
/ (8. * N);
};
template <>
struct I0ATerm<0> { // 1/sqrt(2*PI);
static const double value =
0.398942280401432677939946059934381868475858631164934657665925;
};
int main(int argc, char **argv) {
I0ATerm<1>::value;
}
Error message from gcc 5.2:
test.cpp: In instantiation of 'const double I0ATerm<1>::value':
test.cpp:12:14: required from here
test.cpp:3:22: error: the value of 'I0ATerm<0>::value' is not usable in a
constant expression
static const double value = I0ATerm<N-1>::value * (2.*N-1.) * (2.*N-1.) / (8.
* N);
^
test.cpp:8:22: note: 'I0ATerm<0>::value' does not have integral or enumeration
type
static const double value =
0.398942280401432677939946059934381868475858631164934657665925;
^
(changing "double" to "int" "fixes" it (but of course that loss of precision is
not always acceptable).
Given the double is a constant expression, I'm not sure this is intended to
break.
