Re: Does std::unique_ptr support self-reset?

From:
SG <sgesemann@googlemail.invalid>
Newsgroups:
comp.lang.c++.moderated
Date:
Mon, 12 Aug 2013 17:16:38 -0700 (PDT)
Message-ID:
<kubnkg$oa6$1@news.albasani.net>
Am 12.08.2013 19:48, schrieb Greg Marr:

On Monday, August 12, 2013 10:23:38 AM UTC-4, SG wrote:

Actually, this looks good to me. It does not support self-reset but it
does not have to according to the standard. What do you think is
non-conforming about it?


It does support self-reset, exactly as does the MSVC implementation
that Daniel Krugler said is non-conforming, because it doesn't
call get_deleter()(old_value) if the old value and the new value
are the same.


Not true. See below.

This is different than the reset() later in the same file, which is

       void
       reset(pointer __p = pointer()) noexcept
       {
         using std::swap;
         swap(std::get<0>(_M_t), __p);
         if (__p != nullptr)
           get_deleter()(__p);
       }

The difference is
         if (__p != nullptr)
vs
         if (__p != pointer())


I think you got confused with the meaning of pointer(). pointer() is not
a function like get() that returns the current address. pointer()
creates a null pointer value because pointer is a typedef for the
pointer type (a typedef from the deleter class IIRC) much like int() is
equal to zero. So,

  if (__p != pointer())

checks whether p differs from a null pointer and not whether __p differs
from the value returned by get().

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