From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-07-27T15:43:41+09:00
Subject: Re: Beginner help needed: use a class def to create new instance

On Tue, Jul 27, 2010 at 6:36 AM, Steve P. <stevepauly@comcast.net> wrote:
> I am attempting to put as much code inside classes as possible, to
> economize the code in the main body. However, how do I create a new
> class instance using only a method defined in a class?
>
> For instance, in the following code, I want to create a new Class
> Character instance named newchar by fleshing out the code in the #'d
> area. Is it possible?
>
> Otherwise, what is best practice?
>
> PS: I realize I can instantiate newchar=Character.new(da da da) from the
> body of the code but that would require the prompting code be there
> also. that would defeat my purpose. I hope I have given this enough
> thought before posting! :-)

Two considerations:

- I tend to separate the domain objects from the code that interacts
with the outside world to gather the data to populate that domain
object (user typing, DB, etc). This way you gain flexibility, being
able to add ways of loading or creating the object without modifying
that class

- If, in any case, you want the interaction with the user in that
class, I would use a class method that returns an instance. If you
have other ways of creating that instance you can add new methods for
each case. For example:


#!/usr/bin/ruby -w

class Character
  attr_reader :chname, :chnick, :chquote
  def initialize(chname,chnick)
    @chname=chname
    @chnick=chnick
    @chquote=String.new
  end
  def addquote(quote)
    @chquote=quote if quote.length > 10
  end
  def self.from_prompted_input
    print "Char name:    ";chname=gets.chomp
    print "Char Nick:    ";chnick=gets.chomp
    print "Char Quote:          ";chquote=gets.chomp
    Character.new chname, chnick,chquote
  end
end

puts Character.from_prompted_input.inspect

What you had in mind couldn't work, because your method was an
instance method, so from the outside you still needed someone to call
Character.new(x,y,z).promptedinput.

Having class methods to instantiate objects of the class in different
ways is a pretty typical idiom, check for example the Date class in
core:

http://ruby-doc.org/core/classes/Date.html

The methods civil, commercial, etc are class methods that return an
instance, constructed in a different way.

Jesus.