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From: bertrand@eiffel.UUCP (Bertrand Meyer)
Newsgroups: comp.object
Subject: Re: Run-time checks, Compile time Checks, and reliability
Keywords: type checking, high reliability, fault tolerance
Message-ID: <526@eiffel.UUCP>
Date: 14 Apr 91 18:25:04 GMT
References: <1991Mar28.161307.6071@cbnewsh.att.com> <27F780E2.1872@tct.com> <1991Apr12.190418.13128@leland.Stanford.EDU>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 37

From <1991Apr12.190418.13128@leland.Stanford.EDU>
by craig@leland.Stanford.EDU (Craig Chambers):

> I was under the impression that [Interactive's implementation of]
> Eiffel uses a slower 
> implementation of message passing than either in-line caching or indirect
> function calls, which (depending on how it's implemented) could get faster
> with more precise type information.

Another case of misinformation about Eiffel and its implementation.

As far as I know, the application of what Mr. Chambers calls
``indirect function calls'' to a language supporting multiple
inheritance was invented by the Eiffel implementation team,
and was part of the first commercial implementation of Eiffel
released at the end of 1986. I remember that several people looked
*very* studiously then at the form of our generated code.

The implementation uses constant-time dynamic binding, with
small overhead over the routine call mechanism in standard
languages (static binding) by building the appropriate routine tables
and indexing through them.

Returning to the original topic of this discussion, it would be
impossible to build these tables at compile time without
the type information provided by the language.

We looked at caching (a variant of which was sketched in Brad Cox's
January 1984 IEEE Software article), but realized quickly that
although it could make sense for a Smalltalk-like typeless language
to decrease the cost of dynamic binding, it was useless for a typed
language where type information made it possible to obtain a much more
efficient implementation .
-- 
-- Bertrand Meyer
Interactive Software Engineering Inc., Santa Barbara
bertrand@eiffel.uucp