Re: Why use new?

From:

Paul Brettschneider <paul.brettschneider@yahoo.fr>

Newsgroups:

comp.lang.c++

Date:

Thu, 27 Mar 2008 20:37:12 +0100

Message-ID:

<ae22f$47ebf76e$5470058e$27827@news.chello.at>

James Kanze wrote:

Paul Brettschneider wrote:

James Kanze wrote:

[...]

But when are there any reason to use new?

Lots. Most of the time, you use new because you need an
explicit lifetime for the object. You create it in some low
level function, in response to an external event, and you delete
it in some other low level function, in response to some other
external event.

I guess with the advent of containers with non-copyable
elements, more and more of those new() calls will be hidden in
std::container::insert() calls and the like.

I'm not sure what containers you're talking about, but I very
much doubt that any of the calls to new would be found in their
insert() functions.

In the scenario I described (a very, very frequent one for
servers, GUI's and probably a number of other applications), the
new is in response to an external event, as is the delete.
Containers don't repond to external events.

My idea was that you will have code like this (totally made up this moment):

Handle open_window(const std::string &title)
{
   extern std::map<Handle, Window> Windows;
   Handle h(Windows); // Generates unique handle
   Window &w = Windows[h];

   w.set_title(title)
   return h;
}

Here the new() is hidden in operator[] of std::map. IMHO new and delete are
low-level functions (or call them operators) and application developers
should not have to care too much about them. But maybe I'm just silly?