Re: can I turn base object into inherited one?

James Kanze <>
Mon, 14 Apr 2008 01:28:35 -0700 (PDT)
On Apr 14, 2:15 am, Ian Collins <> wrote:

alexl wrote:

I have 2 classes,

class base {
some virtual functions

class derived : public base {
derived(base* b);

is there a simpler way to turn a base object into derived
than the following

base* b = new base();

b->do some stuff

now he becomes derived

base* d = new derived(b);

No, a Base is a Base. You can't morph it into something else.

You can simulate this sort of behavior, however, with a
variation of the letter envelop idiom. Typically, of course,
this idiom is only used to give polymorphic behavior to an
object with value semantics, but since value semantics include
assignment, with the target object acquiring the dynamic type of
the assigned object, the potential is there.

James Kanze (GABI Software)
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