Question : Pickaxe example

ruby-talk
1

I'm reading through part 1, blocks and iterators section. Lots to
digest here :slight_smile:
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',
聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽'Mothers Little Helper', 'Jumpin Jack Flash']
聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽for i in 0...myarray.length

聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽puts myarray.length # added in to debug
聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽puts 'here is i: ' + i.to_s # added in to debug

聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽return myarray[i] if title == myarray[i].title
#leaving .title in causes an error

聽聽聽聽聽#about undefined method
聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽puts 'here is myarray[i] ' + myarray[i]
聽聽聽聽聽聽聽聽聽聽聽聽聽聽end
聽聽聽聽聽聽聽聽聽聽聽聽end

聽聽聽聽聽聽聽聽聽聽聽聽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

2

I'm reading through part 1, blocks and iterators section. Lots to
digest here :slight_smile:
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.

路路路

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

3

Thank you , that helps! The part that was throwing me was the 'Ruby
Tuesday' myarray[0], I'm gathering since it's the first to come before
the puts statement it shows.

Stuart

路路路

On 7/7/06, Matthew Smillie <M.B.Smillie@sms.ed.ac.uk> wrote:

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

> I'm reading through part 1, blocks and iterators section. Lots to
> digest here :slight_smile:
> 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.