On 19/09/2006, at 6:34 PM, Erik de Castro Lopo wrote:
I also suspect that the flexibilty you see in Perl/Python/Ruby
has little to do with dynamic typing and has much more to do with
Perl/Python/Ruby being high level languages in comparision to
the statically typed languages you know like C/C++/Java.
Yeah, I think the power you get from Perl/Python/Ruby is actually due
to two language runtime features that are totally orthogonal to
dynamic typing:
1. A rich reflection/introspection API[1], and
2. Forwarding a method call on a non-existent method name on to a
method[2].
The two features, combined, grants huge power, and I these two
features are what's missing from the mainstream languages. As an
example, I think all of Rails's really cool features (e.g. active
records) rely heavily on both these features. If you stripped out
Perl/Python/Ruby's method forwarding facilities and their reflection
API, what you have is a pretty boring language indeed.
You can do both of these things in a statically typed environment;
it's just that the static type camp hasn't seem to have acknowledged
how useful these facilities are for making long-lived, extensible
programs. Java is the only language I know off the top of my head
that is statically typed and has a reflection API, but it still
doesn't let you have feature (2) above, and its reflection API is
cumbersome to use. C++ has Run-Time Type Information (RTTI), but
that's so featureless that it's practically useless. I'd love to see
a language with a static type system as powerful and useful as
Haskell's with a reflection API that's as powerful as Perl/Python/Ruby.
1. Reflection/introspection means that you can get information about
a class or method at runtime: you can find out what method names are
implemented by the class, what their types are, call them, etc.
Highly dynamic languages will let you add new methods, replace a
class's method implementations with your own implementation, etc.
2. e.g. Objective-C has a method named forwardInvocation that gets
called if you invoke a non-existent method on an object;
forwardInvocation can then do what it likes with the method call,
such as pass the method call on to another object.
--
% Andre Pang : trust.in.love.to.save <http://www.algorithm.com.au/>
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