Re: vector of const references. Is it possible?
Dave Rahardja wrote:
On 8 Mar 2007 13:38:09 -0800, "mlimber" <mlimber@gmail.com> wrote:
Probably not. As least not individually. It requires a pointer to some
memory. IIRC, TR1 specifies that it even must be contiguous memory.
Whether that actually is a pointer to type (or to array of type), or
merely
a void *, that's an implementation detail. What's probably happening
behind the scenes is that the vector allocates "sizeof(type) * capacity"
bytes of memory, and uses placement new in each position that holds a
valid object.
From a vector user's point of view, all that is required is that the
type contained in the vector is copy constructable and assignable (and
that the constructed/assigned to object is the same as the original,
which is why
auto_ptr can't be stored in STL containers). There are no pointers
anywhere in sight.
I don't doubt that you're right in theory, but in practice every STL
implementation I've seen uses pointers to the containee internally and
an error in that regard pops up if you try something like what the OP
suggested.
There are ways to make assignable and copy-constructable objects that
/behave/ like references.
No there isn't: unfortunately, the dot operator is not overloadable. If
there was, containers for polymorphic objects would be much less of a
problem.
See boost.Ref for instance.
Does not cut it either:
#include <boost/ref.hpp>
struct X {
void inc ( void ) {}
};
int main ( void ) {
X value;
X & ref = value;
ref.inc();
boost::reference_wrapper<X> ref_w ( ref );
ref_w.inc(); // fails
}
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