RE: [GD-General] Multiple Inheritance and RTTI

[Jay W. <woo...@Ro...>]

With a single virtual call to a parameterless Render function, there's =
not an advantage.  But in other situations and/or for other reasons, a =
QueryInterface style does have advantages:

1) When you want to call multiple functions offered by a single =
interface, you can query once, test once, then call many times with =
impugnity.  That's quite possibly more efficient than calling a bunch of =
potentially-empty virtual stubs.

2) Using a QueryInterface style allows you to avoid making the function =
call entirely.  If you use many virtual functions in place of an =
interface, and if the functions take many parameters, you'll still have =
to spend time pushing those parameters onto the stack, even if the =
function turns out to be just an empty stub.  (Compiler gurus please =
correct or clarify, but I'm sure this is usually true.)

3) At development time, you won't have to alter the virtual base class =
every time you want to add new functionality.


> -----Original Message-----
> From: Peter Dimov [mailto:pd...@mm...]
> Sent: Wednesday, February 05, 2003 1:25 PM
> To: gam...@li...
> Subject: Re: [GD-General] Multiple Inheritance and RTTI
>
> What are the advantages of this approach over just providing=20
> a (possibly empty) render() in every node type? A virtual call can =
never=20
> lose to a QI + test + potential call.