Message-ID: <388F70EF.CB0CEFF4@caresystems.com.au>
Date: Thu, 27 Jan 2000 08:10:55 +1000
From: leon <Leon AT caresystems DOT com DOT au>
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To: djgpp AT delorie DOT com
Subject: djggp and virtuality
References: <s8s2p3oo7q556 AT corp DOT supernews DOT com>
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Reply-To: djgpp AT delorie DOT com

Hello just have a simple question re how DJGPP deals with virtual methods
:
there is a BaseClass with virtual method VirtualMethod
we also have DerivedClass which overrides VirtualMethod.

suppose somewhere in code i have a pointer to BaseClass (_myBaseClass) which in
fact is assigned an instance of DerivedClass.
Now if i call _myBaseClass->VirtualMethod();
in terms of pointer deref. what is happenieng?

1) _myBaseClass is dereferenced.

i know that more or less compiler has v-table.. so sorry if am wrong...

2) VirtualMethod (like any method of a class) is a contant pointer to method's
code - so we need to derefence this const pointer
3) this const pointer in case of a virtual method points to v-table - so we need
to dereference another pointer (ie to the v-table)
4) v-table contains a pointer to the actual method - so we dereference the
pointer again...]

now my question is - if in DerivedClass VirtualMethod was also made inline - by
calling _myBaseClass->VritualMethod() would steps 3 and 4 be eliminated - i mean
once the class is created - any virtual method needs not to look at the pointer
of v-table at RUNTIME - or may be not?
I mean would compiler be able to optimise any of the above deref. stuff?

if there is so much of pointer deref. - could one "emulate" virtuality via the
fact that const pointers can be initialised at the constructor stage - thus
something like that:
DerivedClass()
:

//here call the BaseClass constructor and tell it to assign the address of
Method to the BaseClass Method ?


{
}

With best regards - Leon.