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From: rpk@rice-chex.ai.mit.edu (Robert Krajewski)
Newsgroups: comp.lang.c++
Subject: Re: Efficient compilation of virtual functions
Message-ID: <10294@life.ai.mit.edu>
Date: 23 Aug 90 22:49:06 GMT
References: <1990Aug22.193347.18486@ux1.cso.uiuc.edu>
Sender: news@ai.mit.edu
Organization: MIT Artificial Intelligence Laboratory
Lines: 19

In article <1990Aug22.193347.18486@ux1.cso.uiuc.edu> nelson@suna2.UUCP (Taed Nelson) writes:
>
>If we have a virtual member function in the base class, and the same member
>  function is redeclared in the subclass, whenever we are using an instance
>  of the subclass, there is _no need_ to consult the virtual function table
>  since we will _always_ call the subclass function.

This does not obtain if you allow separate compilation.  A virtual function
call can only be resolved statically (that is, by the compiler), if
it knows that the subclass really lies at the end of the tree (i.e.,
none of *its* subclasses implements the same virtual function).

A linker could do this sort of thing if it was given the entire class
tree to look at during the link process.  A compiler could do it if
you told it that the class tree that it knew about was the whole
enchilada.

Robert P. Krajewski
Internet: rpk@ai.mit.edu ; Lotus: robert_krajewski.lotus@crd.dnet.lotus.com