Re: why isn't there a placement delete syntax

From:

"Nick C" <nick@google.com>

Newsgroups:

comp.lang.c++.moderated

Date:

29 Sep 2006 08:41:19 -0400

Message-ID:

<451ce772$0$21345$db0fefd9@news.zen.co.uk>

<andrew_nuss@yahoo.com> wrote in message
news:1159281072.127775.183840@b28g2000cwb.googlegroups.com...

Hi,

I have created an interface with placement new that uses a Heap
reference that supplies Alloc/Free functionality. The compiler forces
the definition of a placement delete. But there is no syntax that I
can find to invoke the placement delete!

struct Object {
   static void* operator new (Heap&, size_t);
   static void operator delete (Heap&, void*);
};

class MyObj : public Object {
   ...
};

main {
   Heap heap;
   MyObj* p = new (heap) MyObj(); // works!
   delete (heap) p; // illlegal!
}

Can anyone explain how to delete these objects. I.e. why doesn't the
obvious analagous invocation of delete work using placement syntax.
What do I do?

Andy

There are some interesting comments here, but funamentally, the ability to
specify a placement delete syntax is an omission. Stroustrop is still
undecided whether this omission was the right choice.

I have seen lots of posters mention workarounds, but there are some cases
that cannot be worked around. An example is a system-wide memory allocation
strategy using placement new. Yes, you can use data encoded on the heap etc
etc.. but in systems where there is more than one vendor of code running,
this is impossible - as another library may already have declared a global
operator delete!

By the way - I would love to be corrected on this as I have battled to
provide such a strategy in C++

Nick Church

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