Some time ago, I needed a trait is_copy_constructible, which is a special case of is_constructible_from. I remeber to have some thought, that if C++ would support injected friends it might be possible to calculate. But that was really tricky solution and I just posponed it until the compilers support injected friends (due to the upcoming standard). At least MSVC 9 supports it now and I think we could try solving it, may be for the first for copy constructible trait and later generalize it.<br>
<br><br><div class="gmail_quote">On Tue, Mar 17, 2009 at 4:50 PM, Steven Watanabe <span dir="ltr">&lt;<a href="mailto:watanabesj@gmail.com">watanabesj@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
AMDG<div><div></div><div class="h5"><br></div></div>
How do you get an expression to have<br>
a different type depending on whether<br>
a given class has a particular constructor?<br>
<br>
In Christ,<br><font color="#888888">
Steven Watanabe</font></blockquote></div><br>