Rails - Jul 2008 - helper functions permanently altering variables

Greetings,

I''m not sure if I''m maybe not understanding the helper
functions
correctly, but I''m having a weird problem that seems like it
shouldn''t
be.  I''m sanitizing some book names for url''s using my
application
helper:

-- application helper

def format_url(url)
    title = url
    clean_string(title)
    truncate(@title, 100, "")
    return title
end

def clean_string(str)
    str.gsub!(/\W+/, '' '') # all non-word chars to spaces
    str.strip!            # ohh la la
    str.downcase!         #
    str.gsub!(/\ +/, ''-'') # spaces to dashes, preferred
separator char
everywhere
end

-- view showing the books

book.product_name
#returns "a name with a lot of spaces and characters in it"

link_to(image_tag(book.image_url_small), :controller => "book",
:action
=> "detail", :book_url => format_url(book.product_name), :key
=>
book.isbn)

book.product_name
#returns "a-name-with-a-lot-of-spaces-and-characters-in-it"

so the problem is I want a function that formats just the path, but what
I have here alters book.product name permanently, so that when I want to
write it as text to the screen after using format_url,
it-has-the-escape-dashes-everywhere-in-it.  how come it alters this when
I pass it as a param, and then variable assign it to "title" and do
all
the alterations on the "title" variable?

Thanks,

Jason
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by the way I notice that the above code is wrong - assume that title and 
@title are consistent throughout the function.
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Jason Pfeifer wrote:
> by the way I notice that the above code is wrong - assume that title and 
> @title are consistent throughout the function.
The easy answer is that in ruby, everything is an object and objects get 
passed by reference, not by value. So when you pass in url to a method, 
and then assign it to another variable (title), that new variable is 
just a pointer to the same memory location as what was passed in. The 
solution is to clone or dup:

title = url.clone

And you should be okay. I may have over-simplified the explanation, and 
if so, someone else might elect to explain it better.

Peace,
Phillip
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> The easy answer is that in ruby, everything is an object and objects get 
> passed by reference, not by value. So when you pass in url to a method, 
> and then assign it to another variable (title), that new variable is 
> just a pointer to the same memory location as what was passed in. The 
> solution is to clone or dup:
Ahhh, ok thanks Phillip! Explanation was good and understood.

I actually solved the problem just recently by doing thus:

title = url + ""

which seems to work and force title not to just remain as a pointer to 
url.

Cheers,

Jason
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Jason Pfeifer wrote:
> I actually solved the problem just recently by doing thus:
> 
> title = url + ""
> 
And if I had to guess (which I do because I don''t feel like digging 
through source), I''d say that under the hood the equivalent of

title = url.clone + ""

is happening. So you could save the one or two processor cycles by doing 
the clone yourself and not worrying about the concatenation.

Peace,
Phillip
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Great thanks for the explanation.  Processing cycles saved.
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