http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55663
Michael Lopez <mlopez at cse dot tamu.edu> changed:
What |Removed |Added
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CC| |mlopez at cse dot tamu.edu
--- Comment #1 from Michael Lopez <mlopez at cse dot tamu.edu> 2012-12-14
21:35:17 UTC ---
I also ran into this bug using GCC 4.8.0 20121121 (experimental) with compile
flags
-std=c++11 -Wall -pedantic -Wextra
Here is a simpler version of the reported bug.
template <typename>
constexpr bool the_truth () { return true; }
template <bool>
struct Takes_bool { };
template<bool B>
using Alias = Takes_bool<B>;
template<typename T>
struct test { using type = Alias<the_truth<T>()>; };
int main () {
test<int> a;
return 0;
}
The compiler is giving me:
main.cpp: In substitution of ‘template<bool B> using Alias = Takes_bool<B>
[with bool B = the_truth<int>()]’:
main.cpp:11:51: required from ‘struct test<int>’
main.cpp:14:13: required from here
main.cpp:11:51: error: integral expression ‘the_truth<int>()’ is not constant
struct test { using type = Alias<the_truth<T>()>; };
^
main.cpp:11:51: error: trying to instantiate ‘template<bool B> using Alias =
Takes_bool<B>’
main.cpp: In function ‘int main()’:
main.cpp:14:13: warning: unused variable ‘a’ [-Wunused-variable]
test<int> a;
^
make: *** [main.o] Error 1
Peeking inside GCC, it seems that the error is thrown from pt.c in
check_instantiated_arg.
Somehow the template constexpr is loosing its "constantness" when expanded in a
dependent context. When the_truth is not a template, there is no error.
