From: Yasushi Shoji <yashi@...>
Date: 2000-10-20T20:17:43+09:00
Subject: [ruby-talk:5707] Re: Dynamic languages, SWOT ?

At Fri, 20 Oct 2000 19:00:06 +0900,
Hugh Sasse Staff Elec Eng <hgs@dmu.ac.uk> wrote:

> That is fine.  However, with dynamic languages one cannot say what
> methods an object has at compile time, because we can extend objects
> at run time.  This makes our code more flexible, because if objects
> don't do what we want we add or override methods.  But it also means
> that we cannot have things like design by contract, because a method
> cannot say much about what it will get as parameters.

# this is class users point of view

IMHO, in order to use a method as a class user, you need to know

- name of the method
- what parameters are required

yes, as you said, we can change methods behavior at runtime, but it's
just "we can", not "depends on computer's mood".

# it's good thing computers still don't have feelings yet ;)

[...]
> It also assists in avoiding duplication of code, and makes things
> extensible as more "subtypes" may be created. But the case statement has
> an "else" (or "default") clause, so unknown types can be picked up.  If
> one has thrown out the case statement, presumably one has to add some kind
> of assertion to check the incoming type, but that would break the dynamic
> nature of the software.  Or would it?

# this is class maintainer's point of view.

I'm not sure this is specific to Ruby only or came form other
language, but it is recommended to use Object#respond_to? to ensure
that the unknown object you have is capable to handle what you want.
# yes, there are different methods with same name.

e.g.

class Some
  def foo(o)
    raise 'oops' unless o.respond_to? :bar
    :
    foo.bar
  end
end

> So is this situation just "one of those trade-offs one has to accept",
> and it can be said that dynamic languages are better at different things
> from strongly typed languages, but they are equally valid, just different?
> Or is there some huge advantage that I have missed, which would make
> the loss of these automatic checks a price worth paying?

IMHO, it's just different. and as usual, both side has pros and cons.

http://www.cyberdyne-object-sys.com/oofaq2/body/typing.htm#S2.4

ps. I'm no way an expert of OO languages. These are just MHO.
--
       yashi