[boost] Re: Proposal: Efficient Pointers

From: Philippe A. Bouchard (philippeb_at_[hidden])
Date: 2002-07-17 04:39:20

> > From: Philippe A. Bouchard [mailto:philippeb_at_[hidden]]
> > "David B. Held" <dheld_at_[hidden]> wrote in message
> > news:ah0cl8$tqu$1_at_main.gmane.org...

[...]

> This usage of 'mutable' was rejected because it has the side effect that
two
> copies of an object are not equivalent.  This, in turn, can cause nasty
> side-effects if you use mutable_ptr with Standard containers and
algorithms.

Yeah I know, this is why 'mutable' was in the class name; to warn developer
from its side effects.

> While you can usually get away with using it in containers (although it's
> not technically portable), the real problem comes in using it with
> algorithms:

mutable_ptr<> should have restricted usages for primitive operations like
container copyings and destructions.  Advantageous example:

class entry
{
    virtual ~entry() {}
};

class company : entry
{
    string name;
    list< mutable_ptr<entry> > affected_contracts;
};

class scientist : entry
{
    string name;
};

list< mutable_ptr<entry> > transactions;

You can see here that you could read a file into a list<> and transform it
into a vector<> when you know its final size.  You'll also notice by
yourself that destructions will be done cleanly.

[...]

Philippe A. Bouchard