Re: C++ boxing

From:

Nick Hounsome <nick.hounsome@googlemail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 14 Feb 2010 19:31:07 CST

Message-ID:

<d6b26663-a6ef-4ae4-86cc-d4196f6a2ed6@f34g2000yqc.googlegroups.com>

On 12 Feb, 22:43, pfultz2 <pful...@yahoo.com> wrote:

Is there a way to box a type in c++ like this:

class Interface
{
public:
virtual void foo() = 0;

};

class A

// derive from interface
class A : public Interface

{
public:
void foo();

};

And then I could box this type like this:
Interface * a = box_cast<Interface*>(new A());

With the changes above

Interface* a = new A;
a->foo(); // calls A::foo

This is just polymorphism not boxing.

boxing is what .NET does to convert struct types (stack allocated in C+
+) to equivalent reference types (heap allocated in C++) and back.

When generic containers came into .NET a lot of the need for boxing
went away and there is no equivalent problem in C++ (in fact with C++
it's harder to manage containers of "reference types" (i.e. heap
stuff) because you haven't got the garbage collection)

The main surviving uses are for reflection type problems and generic
Object.ToString stuff and you haven't given enough info for us to know
why you think that you need it.

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