From: Daniel N <has.sox@...>
Date: 2007-02-26T12:13:17+09:00
Subject: Re: Methods and :parameters

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On 2/26/07, Pedro Del Gallego <pedro.delgallego@gmail.com> 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"


When you use this kind of argument for a method it is encapulated into an
anonymous hash.  It's like writing
add_book( { :title=>"El quijote", :author=> "Miguel de Cervantes",
:tag=>"novel" } )


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



You've added the attr_writer, but you may want to make it into an

attr_accessor

so that you have both reader and writer


Your add_book should look something like, can't give it to you exactly.
sorri no ruby at work :(

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

Since book is an Hash, you need to access it as book[:title].  You need to
assign the book[:title] given to the book object to its own title, the one
you made the accessor for.

I must say though that I don't quite understand how you can add_book to a
book.  I would expect to see this as part of an initialize method instead.
That way you would write

book = Book.new( :title => 'bla', :author => 'author' )

But that's just me.

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


What this does is sets the local variable book, inside the add_book method
to an empty array by default.  ie if there is no parameter passed then you
can rely on it being an empty array.

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