This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
[Voted into WP at March, 2010 meeting.]
7.7 [expr.const] permits literal types with a constexpr conversion function to an integral type to be used in an integral constant expression. However, such conversions are not listed in 13.4.3 [temp.arg.nontype] bullet 5.1 among the conversions applied to template-arguments for a non-type template-parameter of integral or enumeration type.
Notes from the March, 2009 meeting:
The original national body comment suggested allowing any literal type as a non-type template argument. The CWG was not in favor of this change, but in the course of discussing the suggestion discovered the problem with template-parameters of integral and enumeration type.
Proposed resolution (October, 2009):
Change 13.4.3 [temp.arg.nontype] bullet 1.1 as follows: