Re: Template metafunction returning pointer-to-member

From:

Yechezkel Mett <ymett.on.usenet@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 25 Sep 2008 15:31:02 CST

Message-ID:

<ae1a7556-f0d0-4244-94e3-a8543d8bcc66@z66g2000hsc.googlegroups.com>

On Sep 24, 5:58 pm, Marsh Ray <marsh...@gmail.com> wrote:

struct sample
{
    float member_one;
};

template <typename T, int N> struct choose_p2mem { };

template <> struct choose_p2mem<sample, 1>
{
    // Error: a member of type "int sample::*const" cannot have an in-
class initializer
    //static int sample::* const ptr2mem = &sample::member_one;

    static float sample::* const ptr2mem;

};

// Error: "float sample::*const choose_p2mem<sample, 1>::ptr2mem" is
not an entity that can be explicitly specialized
template <>
float sample::* const choose_p2mem<sample, 1>::ptr2mem =
&sample::member_one;

It's nothing to do with the ptr-to-member; the same thing would happen
with any type. Try the following:

float sample::* const choose_p2mem<sample, 1>::ptr2mem =
&sample::member_one;

(without the "template <>").

The point is that "choose_p2mem<sample, 1>" is not a template; it's a
full specialization, which is just a plain class. Note that this
definition will need to go in a cpp file, not a header file, like all
class member definitions.

Yechezkel Mett

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