Re: OO, C++, and something much better!

[Eric Clayberg <clayberg@parcplace.com>]

Fergus Henderson wrote:
> Alan Lovejoy <alovejoy@concentric.net> writes:
> >When typing errors only constitute 2% or less of all errors, it's time
> >to check the cost of eliminating the final 2% of the problem.
> My experience is that errors caught by type checking constitute a LOT
> more than 2% of errors.
> For a period of time I carefully recorded the cause of every error that
> I found while writing a Mercury program.  Of the 155 errors that I
> recorded, 73 were error caught by the type checker.

If anything, I think that reflects poorly on the syntax of whatever
language you were using. The more "rules" a language has, the more
involved its syntax, and the more draconian its type system, then the
more type errors are likely to be created by the developer and then
caught by the compiler. In a language like Smalltalk which has an
absurdly simple, consistent syntax, and which has a very open-mined
concept of "type", very few type errors are ever created to begin with
and thus very few actually exist to be found. The *few* real type errors
that are created tend to be caught almost immediately by Smalltalk's
superb debugging facilities.

Having been involved with commercial Smalltalk development for quite a
few years, I tend to agree with Alan that the percentage of actual type
related errors in Smalltalk programs is less that 2% - far less in my
experience. I have written over several hundred thousand lines of
commercial Smalltalk code and have been involved in several dozen large
Smalltalk projects (ranging from 100,000 lines of code and up). In all
that time, I have only run across a handful of true type errors (of the
nature that a static type checker would catch). The Smalltalk language
is very simple and very flexible and makes a lot of things perfectly
legal that would not be allowed in, say, C++. Most "message not
understood" errors, in fact, are to the nil object in Smalltalk (the
moral equivalent of a null pointer in C). These are not really type
errors, but usually problems with improper initializations or premature
discarding of data. These are logic problems; not type problems. A
static type checker would catch them no better in Smalltalk than it
would in C++.

I am amazed at the level of hubris evidence in this discussion. Folks
are jumping in and making assumptions about how Smalltalk works based
upon how their favorite statically typed language works. Smalltalk has
very different rules than what are common in most statically typed
languages. Smalltalk simply doesn't need static type checking. If you
have any doubts about that, then you should try it out yourself. You can
download Smalltalk Express (a fully function, 16-bit Windows Smalltalk
IDE) for free from http://www.objectshare.com.

-Eric