From: Christoph Rippel <crippel@...>
Date: 2001-03-24T15:03:52+09:00
Subject: [ruby-talk:13164] Re: Static versus dynamic typing [long]


> From: Benjamin J. Tilly [mailto:ben_tilly@operamail.com]
[...] 
> My summary would be that a type system is a spec, and the type
> checks are tests of the spec.  To get a sense of how much a
> type system really buys you, compare how much of the spec
> really matters versus how much of that spec is described in
> the type system.  The difference is how much the type system
> did not do that you wanted.

That's a pretty nice and concise summery. I thought that  the 
discussion was very interesting but that it's focus was too much 
on type signatures of the methods etc. because in principle that
``just'' a question of single versus multiple dispatch which is 
possible in a dynamic and static world. The issue of type mutating
capability of a language (the point which Ruby sooo attractive 
and where Java gives the worst of two possible worlds) was bit a 
left out IMO. 
 
> What is the worst of all worlds is a test you cannot trust. 
> Given that type systems don't actually catch the kinds of
> errors that really matter, but people think the type system is
> catching their errors, they lend themselves to a lazy way of
> thinking.

In a way all testing regimes are like this - if you are not aware
of its limitation you will be always in trouble. 

Christoph