Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!mcsun!sunic!tut!tukki!sakkinen
From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.lang.misc
Subject: Re: An Interesting View of "Strong" Vs. "Weak" Typing
Message-ID: <2653@tukki.jyu.fi>
Date: 10 Jan 90 08:25:42 GMT
References: <7049@tank.uchicago.edu> <16678@megaron.cs.arizona.edu>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
          SAKKINEN@FINJYU.bitnet (alternative)
Organization: University of Jyvaskyla, Finland
Lines: 38

In article <16678@megaron.cs.arizona.edu> gudeman@cs.arizona.edu (David Gudeman) writes:
>In article  <7049@tank.uchicago.edu> keith@curry.uchicago.edu (Keith Waclena) writes:
> [...]
>> [...]
>>I would say that C is weakly typed (or untyped) dynamically, and
>>strongly-typed (but not too strongly) statically...
>
>This last sentence bothers me.  It would be quite simple to implement
>a C operator such as "(typeof) x" that returns some representation of
>the type of the variable x.  Granted this operator _does_ have to
>refer to the type information gathered at compile time (it probably
>would be treated as a compile-time constant, like "(sizeof) x"), but
>the type of x is still available at run-time.

I think Waclena's original characterisation is accurate.
Gudeman is thinking about what C could be if it was different!
The semantics of C is very heavily based on the premise that
there is no run-time descriptive information associated with
any programme objects. So, if one extended C with a 'typeof'
operator, an expression like "typeof *p" could only give the base type
of p, _not_ the type of the object to which p points at run time.

One reason why I do not consider C++ a good object-oriented language
is that the above characterisation holds for C++ as well.
Even it keeps no run-time type information except for the bare minimum
needed to handle virtual functions.

There _are_ strongly/statically typed languages that also have complete
run-time type information and a 'typeof' operator. One example is the
object-oriented language Mode, created by Juha Vihavainen at the
University of Helsinki (vihavain@uhecs.helsinki.fi).

Markku Sakkinen
Department of Computer Science
University of Jyvaskyla (a's with umlauts)
Seminaarinkatu 15
SF-40100 Jyvaskyla (umlauts again)
Finland