http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56041
Bug #: 56041
Summary: Constexpr conversion function definition not found in
template argument context
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: webrown....@gmail.com
Created attachment 29215
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29215
C++11 metaprogramming experiment
Enclosed code fails to compile, but should.
Tested with:
g++-mp-4.7 (MacPorts gcc47 4.7.2_2) 4.7.2
g++-mp-4.8 (MacPorts gcc48 4.8-20130113_0) 4.8.0 20130113 (experimental)
Compiled via:
g++-mp-4.7 -O3 -std=c++0x main.cc
g++-mp-4.8 -O3 -std=c++0x main.cc
Use of expression true_type{} as template argument corresponding to bool
template parameter produces diagnostic:
'constexpr integral_constant<T, v>::operator T() const [with T = bool; T v =
true]' used before its definition
[The syntax variant true_type() [note parentheses instead of braces as shown
above] is correctly diagnosed, applying 14.3/2. This variant, as well as a
C++03-style variant, are present but commented out in the attachment; I left
them for possible additional experimentation.]
Using braces should force interpretation as an expression, not a type. That
expression should result in a default-constructed temporary object of the named
type; that type, defined earlier in the source, has a conversion operator
defined inline. However, the compiler claims that the operator's definition is
not yet defined at the point of (implicit) use.
