From: Ken Bloom <kbloom@...>
Date: 2007-02-27T00:10:06+09:00
Subject: Re: Methods and :parameters

On Mon, 26 Feb 2007 10:57:59 +0900, Pedro Del Gallego wrote:

> Hi all,
> 
> I've a question about the :parameter notation. I want to write a method
> that can hold several optional paramters
> 
> add_book    :title=>"El quijote", :author=> "Miguel de Cervantes"
> add_book    :title=>"El quijote", :author=> "Miguel de Cervantes",
> :tag=>"novel" add_book    :title=>"El quijote"
> 
> and i had  write the add_book mehod like this :
> 
> class Book
>    attr_writer :title, :author
> end
> 
> def add_book (book )
>    puts "title : #{book.title} -- Author : #{book.author}"
> end
> 
> but the interpreter said : ./bibliom.rb:7:in `add_book': undefined
> method `title' for {:title=>"El quijote", :author=>"Miguel de
> Cervantes"}:Hash (NoMethodError)
> 
> I also try to put a hash object in the incoming parameter, like that :
> 
> def add_book (book=[])  .... end
> 
> My question is how can i wirte a method with several optional parameter
> and then acces they inside of the mehotd ?


def add_book (book )
   puts "title : #{book[:title]} -- Author : #{book[:author]}"
end

When using the named parameter idiom, all of the named parameters are 
lumped together into a single hash which is passed as the last parameter. 
There's no point in defining the Book class -- it won't be used by this 
idiom.

If you want to access the parameters as members, then you can construct 
an OpenStruct inside the method, like so

require 'ostruct'

def add_book book
  book=OpenStruct.new(book)
  puts "title : #{book.title} -- Author : #{book.author}"
end

but that's most likely overkill.

-- 
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/