On 11/14/2014 12:48 AM, David Blaikie wrote:
> My guess is that the proposal was written assuming a certain implementation
> of constexpr that never panned out.
>
> It looks like both GCC and Clang expect constexpr member variables to be
> explicitly marked static:
>
> const.cpp:5:19: error: non-static data member 'f' declared 'constexpr'
> constexpr foo f{};
> ^
>
> (is GCC 4.9's diagnostic - for a simple non-template constexpr member
> variable)
>
That's sad because, as n3651 says on pp. 2-3:
The main problems with “static data member” are:
• they require “duplicate” declarations: once inside the class
template, once outside the class template to provide the “real”
definition in case the constants is odr-used.
• programmers are both miffed and confused by the necessity of
providing twice the same declaration. By contrast, “ordinary”
constant declarations do not need duplicate declarations.
Also, the clang status page:
http://clang.llvm.org/cxx_status.html
reference n3651 below the section title:
C++14 implementation status
Hence, I thought that's what clang implemented.
In addition, the latest standard *draft*:
https://isocpp.org/files/papers/N3797.pdf
contains the n3651 matrix_constants example on p. 313.
Is there some more current standards document which requires the
static qualifier on variable templates within a class?
TIA.
-regards,
Larry
> On Thu, Nov 13, 2014 at 8:38 PM, Larry Evans <cppljev...@suddenlink.net>
> wrote:
>
>> The following code:
>>
>> //{=======================================
>> #include <type_traits>
>> struct variable_template
>> {
>> template <int Value>
>> std::integral_constant<int,Value> constexpr
>> value{}
>> ;
>> };
>> #include <iostream>
>> #include <iomanip>
>> int main()
>> {
>> std::cout<<
>> variable_template::
>> value<1>()<<std::endl;
>> return 0;
>> }
>> //}=======================================
[snip]
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