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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Static vs. Dynamic typing again (was Re: OO, C++,
 and something much better!)
Date: 1997/01/30
Message-ID: <E4t2ML.IqG@world.std.com>#1/1
X-Deja-AN: 213263477
references: <JSA.97Jan16141937@alexandria>
 <01bc0a1e$faed8ce0$c318b993@jarvisb> <E4L15n.GnC@world.std.com>
 <5covaj$l0@boursy.news.erols.com>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.smalltalk,comp.lang.eiffel,comp.lang.ada,comp.object
Date: 1997-01-30T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <5covaj$l0@boursy.news.erols.com>,
Damon Feldman <feldmand@erols.com> wrote:
>Statically typed means that types are *determined* at compile time.
>Dynamically typed means types are *determined* at runtime.
>
>Static type *checking* means checking done at compile time.
>Dynamic type *checking* means checking at run time, I suppose.

OK.

>"Checking" catches errors, "determining" types determines what class a 
>variable is (and therefore how it handles messages and what data it has access 
>to).

OK.

>But dynamically typed languages just generate errors rather than explicitly do 
>dynamic type-checking.  (This is a bit of a simplification, but that's the 
>idea.) 

Heh?  Smalltalk does a type check on the *target* of the message.  It
does not do a type check on the (other) parameters of the message.

>So Smalltalk is dynamically typed because objects can get different types at 
>runtime depending on execution,

This is true of Ada tagged types, and Eiffel types, too.

>... even though it is not type checked 
>explicitly beyond generating an error or automatically expanding collection 
>sizes, etc.

My point was that the difference between Ada/C/C++/Eiffel and Smalltalk
is not merely *when* the checks are done (compile-time vs. run-time),
but that Smalltalk does fewer checks.  In particular, it does not check
the type of each parameter of a message (not at run time, not at compile
time).  So, it's wrong to view the difference between these languages as
compile-time-type-checks vs. run-time-type-checks.

- Bob