From: Ilan Berci <coder68@...>
Date: 2007-04-04T00:27:55+09:00
Subject: Re: New presentation on Ruby

Chauk-Mean P wrote:

> 
> As stated in slide 15 :
> - I just said that Java untyped collections or generic collections for 
> type
> Object DO support heterogeneous types.
> But the drawback is that you NEED to downcast a retrieved element.
> - Conversely, if you use a generic collection for a type X (e.g.
> TalkingAnimal) different than Object, you can put only objects of type 
> X.
> You cannot put an object that is not of type X (e.g Rabbit2)
> You avoid most downcasts for retrieved elements. Thus you can retrieve a
> TalkingAnimal and call talk.
> But if you put an object of type Y that extends the capability of X
> (e.gDuck2) and you want to call a method of Y (
> e.g. walk), then you need to downcast to Y.
> 
> Tell me what is wrong about that ?
> 


Chuck, please update your java from 1.4 to 1.5JDK (5.0) and check out 
generics, there is no longer a NEED(why the upercase?)  to downcast from 
containers as it's done for you.  It is a far cry from c++ templates 
that are done at compile time but it still alleviates the need for 
downcasting.

class SomeThing
{
}

java.util.Vector<SomeThing> noNeedForDownCastingVector = new 
java.util.Vector<SomeThing>;

for your viewing pleasure: http://java.sun.com/j2se/1.5.0/docs/api/

I also fully realize that I didn't hear the talk that went with the 
slides but you asked us for feedback on the slides knowing that we 
didn't hear the presentation.  Be carefull what you wish for especially 
on this list..

As for your example on duck typing, I can illustrate the same thing in 
your slides by doing an exact port in Java which is known not to support 
duck typing (message passing)

class Duck
{  public String quack() {return "quack";} }

class Bird
{  public String quack() {return "chirp";}}

d = new Duck(); d.quack();
b = new Bird(); b.quack();  //  does this mean java supports duck typing 
too?? It does if we go by your slide

or C++
struct Duck { void quack() {cout << "quack";}}
struct Bird { void quack() {cout << "chirp";}}
Duck().quack(); Bird().quack();  // Wow.. guess this means c++ supports 
duck typing too..

i.e. My point was in order to illustrate the construct, you must use a 
temporary variable!

As for private methods in class Object, you are correct sir and I stand 
corrected..

As for Erlang, it has simply nothing at all remotely to do with Ruby. 
It's a seperate beast entirely and it appeared from your slide show that 
you were utilizing it to promote Ruby based on a small subset of 
functional programming.  It's kind of like saying that the language Ruby 
is spelled exactly like the gem and we all know how shiny the gem is so 
Ruby must be shiny by extension.  Actually come to think of it, I think 
Ruby has more in common with a gem than it has with Erlang.

I experimented with Erlang from the urging of my former boss and 
suffered from severe headaches, brushes with suicide, weight gain and 
halitosis..   I am hoping the new pragmatic book will enlighten me but 
one thing I can atest to is that it's far removed from Ruby and the only 
time thy should be used in a sentence together is the following:
"Ruby starts with an 'R' and Erlang starts with an 'E' "


ilan

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