From: Eric Mahurin <eric_mahurin@...>
Date: 2005-08-09T02:21:57+09:00
Subject: Re: polymorphism and/or named parameters: the ruby way?

--- "Berger, Daniel" <Daniel.Berger@qwest.com> wrote:

> > -----Original Message-----
> > From: Stephan Mueller [mailto:d454d@web.de] 
> > Sent: Saturday, August 06, 2005 12:01 PM
> > To: ruby-talk ML
> > Subject: polymorphism and/or named parameters: the ruby
> way?
> > 
> > 
> > Hello,
> > 
> > i am kind of a newbi, please forgive me if i am asking
> stale 
> > questions.
> > 
> > I want to adjust the initialization of an object according
> to 
> > the parameters given to new.
> 
> A typical idiom for constructors is to do "yield self if
> block_given?",
> which I prefer over hash based arguments.  For example:
> 
> class Foo
>    attr_accessor :bar, :baz, :zap
>    def initialize
>       yield self if block_given?
>    end
> end
> 
> foo = Foo.new do |f|
>    f.bar = "hello"
>    f.baz = 5
>    f.zap = "world"
> end

What's the advantage of this over:

foo = Foo.new
foo.bar = "hello"
foo.baz = 5
foo.zap = "world"

Is it method chaining?  You want this thing to return foo?  You
could just end this statement list with "foo", or you could use
"ensure":

begin
  foo = Foo.new
ensure
  foo.bar = "hello"
  foo.baz = 5
  foo.zap = "world"
end

This begin..ensure..end expression returns foo (the result
before ensure) not "world" as you might expect.  Great for
doing post operations after you calculate a return value
(equivalent of C's i++ is another example).



		
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