Re: Restricting instantiation of the object in heap only for the particular case
WittyGuy wrote:
My class looks something like this:
class Base
{
public:
Base () {}
~Base () {} // No virtual dtor in the base class
private:
};
class Derived :
public Base
{
public:
Derived () {}
~Derived () {}
private:
};
int
main ()
{
Base *pB = new Derived; // how to *restrict* this type of
instantiation
delete pB;
Undefined behaviour.
Derived *pD = new Derived; // Should allow this type of
instantiation
delete pD;
OK.
return 0;
}
As given in the above sample code, how to restrict the instantiation
of derived class object in the heap when it's assigned to a Base class
pointer rather should allow the same if it's assigned to pointer of
same type.
Huh?... If your base class is not declared 'protected' or 'private',
the conversion from any pointer to derived to a pointer to base is
valid. There is no way for the compiler to know where the pointer
comes from to restrict such conversion. You, and only you, can do
that by declaring protected or private inheritance:
class Derived : protected Base {};
Coz the later form of instantiation can be allowed as there
is no harm of memleak though virtual dtor is not defined in base
class.
If all you want is to prohibit implicit derived-to-base conversion,
make your base class protected or private.
Basically this query araised coz, I'm inheriting from stl container.
In most cases it would be recommended to derive privately and then
reimplement all the necessary functionality in terms of the base
class.
Yes I know ideally I shouldn't have done this coz STL container's dtor
are not virtual dtor. But anyways if there is a way of restricting the
instantiation of object as explained above, it should solve my
problem.
No. Public inheritance *means* conversion of pointer (or reference)
to derived to pointer (reference) to base is allowed.
V
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