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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: <524@eiffel.UUCP>
Date: 7 Apr 91 17:16:59 GMT
References: <1991Mar28.161307.6071@cbnewsh.att.com> <27F780E2.1872@tct.com> <1991Apr7.013813.23513@leland.Stanford.EDU>
Organization: Interactive Software Engineering, Santa Barbara CA
Lines: 39

From <1991Apr7.013813.23513@leland.Stanford.EDU> by craig@leland.Stanford.EDU
(Craig Chambers):

> In a non-object-oriented language (at least one with a good type system)
> types specify interfaces (plus possibly some behavioral specifications)
> to objects, but specifically attempt to abstract away from specifying
> anything about implementations/representations of the objects of
> particular types (to support more reusability of code).
> This means that such interface-level types provide little information
> for a compiler to use to optimize messages sent to such objects.
> So the standard argument that static type information speeds execution
> of programs does not apply to object-oriented languages
> (or at least does not apply to anything near the degree it does
> in non-object-oriented languages).

This runs contrary to our experience. To handle a routine
call

    x.f

with polymorphism on x and dynamic binding on f, it helps the
compiler considerably to have the type information resulting
from the declaration

    x: SOME_TYPE

which indicates that the objects to which x may be
attached at the time of the call are not arbitrary,
but must be instances of SOME_TYPE (that is to say,
direct instances of SOME_TYPE itself or of one of its
descendants).

By restricting the scope of possible types (classes), this
information enables the compiler to handle calls in a much
more efficient way than otherwise.

-- Bertrand Meyer
Interactive Software Engineering Inc., Santa Barbara
bertrand@eiffel.uucp