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From: budd@orstcs.cs.ORST.EDU
Newsgroups: comp.lang.smalltalk
Subject: declarations vs smalltalk
Message-ID: <245100009@orstcs>
Date: Mon, 29-Jun-87 13:50:00 EDT
Article-I.D.: orstcs.245100009
Posted: Mon Jun 29 13:50:00 1987
Date-Received: Wed, 1-Jul-87 06:48:06 EDT
Lines: 39
Nf-ID: #N:orstcs:245100009:000:1999
Nf-From: orstcs.cs.ORST.EDU!budd    Jun 29 10:50:00 1987


I may be showing my vast ignorance again, but somehow I just don't see how
adding type declarations to Smalltalk helps anything.  It would seem as if
one of the following cases must apply

1. The C philosophy - the user can give declarations, but these are not
checked at run time.  You pass something that doesn't match the
declaration, your program will crash and burn.  Not very nice.

2. The Pascal philososphy - declarations are all checked statically at some
point long before run time.  Either requires declarations everywhere (too
restrictive and limits polymorphism) or requires extensive data flow
analysis (complicated).

3. Hidden code is created to check the conformability of argument types
with declarations prior to method execution.  Why is this any more
efficient than user written code to do the same task?  Allowing the user to
do it would seem to be more flexible.  And what happes when the
declarations are violated?  Does the user have any recourse?

4. Types are considered as part of the message pattern for the purposes of
method lookup.  (This is an extension of object message lookup, where the
types of arguments other than the first may also be important).  This would
seem to be the most general solution, since the only overhead involved is
that of method lookup, not argument checking, and tricks such as caching
can be used to speed up message lookup.  Never the less, the Smalltalk
notion of class is not the most useful concept of type that could be
envisioned, and again this limits polymorphism.

In short, there seems to be an implicit conflict between strong typing, or
typing of any sort, and polymorphism.  Strengthing one limits the other.
Smalltalk has come down strongly on
the side of polymorphism, and even I (Smalltalk heretic than I am) have a
hard time imagining anything similar to Smalltalk that changes this.

I am looking forward to hearing how I am all wrong, and how option number 5
makes all problems go away.

--tim budd (budd@oregon-state)