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From: Windflower Waters (WWaters_at_[hidden])
Date: 2007-05-01 10:08:55
This is what I would do:
Main()
{
shared_ptr<B> poly(new B); // Start with a pointer that matches the
type
MyFunction( dynamic_pointer_cast<A>(poly) ); // Cast it in the
argument list
}
-- Windflower
-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] On Behalf Of Hughes, James
Sent: Tuesday, May 01, 2007 4:19 AM
To: Boost-users_at_[hidden]
Subject: [Boost-users] [Shared_ptrs] As I doing this right
Although I have been using shared_ptr's for a while, I still get a bit
confused with polymorphic stuff ...no change there.
An pseudocode example:
Class A
{
};
Class B : public A
{
DoStuff1();
DoStuff2();
DoStuff3();
DoStuff4()
};
// MyFunction handles A and classes derived from A
MyFunction(shared_ptr<A>)
{
};
Main()
{
shared_ptr<A> poly<new B); // OK so far
MyFunction(poly); // Still OK -
// OK, done this, but now if I want to call a load of stuff in an
instance of B
// I either have to make a load of pointer casts (because poly is an
A)
dynamic_pointer_cast<B>(poly)->DoStuff1();
dynamic_pointer_cast<B>(poly)->DoStuff2();
dynamic_pointer_cast<B>(poly)->DoStuff3();
dynamic_pointer_cast<B>(poly)->DoStuff4();
// Or this?
shared_ptr<B> tmp = dynamic_pointer_cast<B>(poly); // is this right?
// I have to create a new pointer?
tmp->DoStuff1();
tmp->DoStuff2();
tmp->DoStuff3();
tmp->DoStuff4();
}
So, the quesiton is one of efficiency - if I was using pointers, I would
just new a B and assign to a B* variable, then pass in to the function
which would use it as an A - no temp required. With above a new tmp
pointer seems to be required - am I right or have I missed something
blindingly obvious.
James
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