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From: zweig@brutus.cs.uiuc.edu (Johnny Zweig)
Newsgroups: comp.lang.c++
Subject: Re: The price of inheritance?
Message-ID: <1989Sep11.002541.13902@brutus.cs.uiuc.edu>
Date: 11 Sep 89 00:25:41 GMT
References: <12581@brunix.UUCP>
Sender: news@brutus.cs.uiuc.edu
Organization: U of Illinois, CS Dept., Systems Research Group
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gjb@cs.brown.edu writes:

>Some recent work I've been doing with C++ and the InterViews
>user-interface toolkit has made me wonder how expensive inheritance
>is. I realize that a virtual function is slower than a non-virtual,
>but does the depth of the class hierarchy affect speed?

>For example, let's say I create:

> [a class with a virtual function that gets redefined in a subclass...]

> [Will the subclass's virtual function be more expensive to call?]

No. Virtual function tables are (as far as I know or can imagine)
flattened -- each (subsubsub...)class just has a big list of pointers. In
the example, the virtual function would just be the value of the nth
(probably 0th) pointer in the v-table. Same banana in the subclass, or
any other {sub}*classes.

-Johnny