[ruby-talk:15041] Re: Ruby Newbie questions

On Sun, 13 May 2001, Sean Russell wrote:

> 	class Date
> 		class << self
> 			def once(*ids)
> 			# ...
> 			end
> 		end
> 		# ...
> 	end

This adds a method to the Date class object, not to instances of
Date.  You call this method using  Date.once()  instead of 
a_date = Date.new;  a_date.once().

No different than saying  def Date.once(*ids)  but arguably more
convienient if you have a bunch of class methods to add.


> Question 2
> 	
> Why doesn't the following do what I'd expect it to, and how does
> one solve this type of problem?
> 
> 	module Child
> 		@level = 0
> 		attr :level, true
> 	end

At the time you are calling @level=, self is the module not an
instance.  Try changing this to:

module Child
	attr :level, true
	def initialize
		super
		@level = 0
	end
end

Applied consistantly, initialize in all included modules will be
called.  BUT, this forces the argument count to be zero, so if you have
arguments to new someone is going to have to call  super()  to get rid of
the args.  You could use  def initialize( *ignored_args )  but that just
moves the problem since Object's initialize takes no args.  I don't know
of a good solution.


> Question 3
> 
> class A ; def initialize ; puts "In A" ; end ; end
> class B < A ; def initialize ; puts "In B" ; end ; end
> b = B.new
> 
> generates:
> 
> In B

The superclass must be called explicitly:

class A ; def initialize ; puts "In A" ; end ; end
class B < A ; def initialize ; super ; puts "In B" ; end ; end
b = B.new


   - Eric B.

--
"What not why"