From: Matthew Smillie <M.B.Smillie@...>
Date: 2006-07-07T21:04:11+09:00
Subject: Re: Question : Pickaxe example

On Jul 7, 2006, at 12:28, Dark Ambient wrote:

> I'm reading through part 1, blocks and iterators section.  Lots to
> digest here :)
> Anyway, there is discussion about implementing a search for songs,
> called 'with_title'
> Even though the first code example is not the one that ultimately gets
> used I think for me it's important to understand it, so I tried
> recreating it outside the actual application. I'm getting some errors
> and would appreciate some feedback.
>
> Here is the code (I've used some puts statements to see what's  
> going on)
>
> def with_title (title)
> myarray = ['Ruby Tuesday', 'Paint it Black', 'Lets Spend the Night  
> Together',
>                'Mothers Little  Helper', 'Jumpin Jack Flash']
>                         for i in 0...myarray.length
>
>                            puts myarray.length # added in to debug
>                            puts 'here is i: ' + i.to_s # added in  
> to debug
>
>                return myarray[i] if title == myarray[i].title
> #leaving .title in causes an error
>
>     #about undefined method

What it does is call the #title method on myarray[i], but in your  
example, myarray[i] is a String, which doesn't have a #title method -  
hence, undefined method.  I believe (my copy is at the office) that  
the example in the book uses a Song class which has the title method  
defined.

>                puts 'here is myarray[i] ' + myarray[i]
>              end
>            end
>
>            with_title('Paint it Black')
>
> If in this line
> return myarray[i] if title == myarray[i].title <------ I removed the
> .title from the right side of
>
> the equality statement, myarray[i]
>
> I get this back:
>
> 5
> here is i: 0
> here is myarray[i] Ruby Tuesday
> 5
> here is i: 1

Which is exactly what I'd expect.  myarray[1] is 'Paint it Black'.   
The next statement after printing 'here is i: 1' is to return the  
current title if it matches the title being searched for.  They  
match, so the method returns.

The usual idiom in Ruby omits explicit return statements, and relies  
on the language to return the value of the final expression evaluated  
in the method.  An explicit return statement exits the method,  
returning the specified value immediately.  In this case, it's used  
as a way to stop the loop once a match is found, presumably with the  
assumption that either you only need the first match, or that only  
one will exist.

matthew smillie.