Re: [Boost-users] [array] VC++ 7.1 bug and a proposed fix

From: Daryle Walker (darylew_at_[hidden])
Date: 2006-07-26 03:43:29

On 7/25/06 2:05 PM, "John Maddock" <john_at_[hidden]> wrote:

> Peter Dimov wrote:
>>> Likewise returning a C-array by value is not legal.
>> 
>> Sorry.
>> 
>> What makes you think that Boost.Array is not intended to be
>> copy-constructable or assignable?
> 
> 'cos I wasn't paying enough attention that's why :-)
> 
> It is assignable, just not copy-constructable (or at least not without a
> core change making arrays copy-constructable).  I wasn't expecting
> copy-construction and assignment to behave differently and it confused me.
> Happens easily :-)

AFAIK, class types with (non-static) array members are _both_ assignable and
copy-constructible.  See section 12.8 in the 2003 C++ standard, paragraph 8
for the copy constructor and paragraph 13 for the assignment operator.  But
you MUST use the implicit copying routines, at least for the copy
constructor, since arrays do _not_ have explicit copying semantics.  This
means that generally you must wrap array members in an private struct if you
need non-implicit construction, using a private static member function that
returns the array's initial value.  See what I did with the
"my_configuration::hook" class in "rational_test.hpp" for an example.

Another part of this thread mentioned assignment operator templates.  Please
remember that C++ does not consider such templates when determining if an
automatically-defined copying assignment operator is needed.  Such an
operator is always a non-template, even if there's a operator template with
a pattern that could match.  If automatically-defined copying assignment
operator won't do what the assignment operator template would, then you must
manually recreate the routine with an explicitly-defined non-template
copying assignment operator.  (A similar rule exists for the copy
constructor, such that it won't consider possibly-matching constructor
templates.)

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com