Re: Reference to void
James Kanze wrote:
Seungbeom Kim wrote:
Allowing reference to void doesn't allow creating an object of type
void; it just allows to refer to an existing object through a supertype.
Reference to Base is allowed even if Base is an abstract base class and
no complete object of Base can exist; in what regard does reference to
void differ?
A reference to Base always designates an object of type Base.
Maybe a sub-object---if Base is abstract, the necessarily a
sub-object. But something of type Base.
Nothing of type void can exist, so the reference cannot refer to
something of type void, not even a sub-object.
Again I'm considering an hypothetical world in which every C++ type is
derived from void. In this case void would be an empty type (do data is
passed to the derived classed), and the compiler disallows to create
objects of types void. But this doesn't imply that the compiler
shouldn't allow object of types derived from void.
If a type (let's name it Derived) is derived from void, and we have an
object of type Derived, we can hold a void reference to that object
because the reference designates a sub-object of our object. It's just
like the following situation:
class Void { /*disallow construction of an object of this type*/ };
class Derived : public Derived {};
Derived d;
Void& r = d;
I still can't see how does Void of this example differs from void in my
assumtion (cannot be instantiated, base of all other objects). Is there
something that I am missing?
What loopholes do you think could it open?
Nothing in particular. Only that it breaks the current
definition of references. I think that it's probably doable,
but it involves a good deal of reflection and work, and I don't
really see any great benefit.
[...]
I think the shoe is on the other foot. You're talking about
messing around with the C++ object model. It's not a question
of "no reason not to"; it's a question of strong reasons for.
And I can't see any.
Ok. Here I must admit that you are right. The benefits are not too
many, and I can't find strong reasons for a C++ change proposal. I was
trying to find out a good reason why references to void aren't allowed,
not to make a change proposal.
Thank you,
Lucian Radu Teodorescu
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