Path: utzoo!attcan!uunet!bu.edu!inmet!stt
From: stt@inmet.inmet.com
Newsgroups: comp.object
Subject: Re: Do we really need types in OOPL's?
Message-ID: <60700003@inmet>
Date: 7 Oct 90 15:32:00 GMT
References: <0yw10qr@Unify.Com>
Lines: 38
Nf-ID: #R:<0yw10qr@Unify.Com>:-19:inmet:60700003:000:1640
Nf-From: inmet.inmet.com!stt    Oct  7 11:32:00 1990


Re: the advantages of static type-checking.

I think there is a fundamental difference between incremental
static checking, and run-time checking.  I whole-heartedly
agree with those who believe an incremental-development
environment is more productive and realistic than a batch-oriented
environment.  However, I still believe that it is critical
that each increment undergo some amount of static checking.

For complex systems, a huge amount of the code is only
conditionally executed, and it is infeasible to exhaustively
test such a system.  The only hope is to get as much help
as possible from static analysis, which looks at every
new line of code prior to run-time, to ensure that
it satisfies all static constraints which have been
established for the system.  

Of course, it is also important
to be able to change the set of static constraints during
the evolution of the system, and when such a change is
made, essentially all existing code of the system must
be reanalyzed.  Again, this should be done prior to
production use, though it is useful if it can be deferred
temporarily, so that all new development need not
come to a standstill.  Doing such massive reanalysis seems
like an excellent use for the millions of workstation MIPS
sitting idle every night.

In general, I would argue that if there are no
machine-enforceable static constraints on a complex
system, then the programmers themselves must have no
idea whether any given line of code is right or wrong,
except through (inherently infeasible) exhaustive testing.

S. Tucker Taft   stt@inmet.inmet.com    uunet!inmet!stt
Intermetrics, Inc.
Cambridge, MA  02138