Newbie question: how to read the "!"

Rails
1

I’m a total beginner at Ruby. I’ve more experience with PHP. I’m trying
to figure out how to read this method:

def empty_cart
@cart = find_cart
@cart.empty!
@items = @cart.items
redirect_to(:action => ‘index’)
end

What does

@cart.empty!

mean?

And does this:

redirect_to(:action => 'index')

mean simply that the action index should be called?

2

On 22/11/2006, at 10:24 AM, Jake Barnes wrote:

What does

@cart.empty!

mean?

Simple. It calls the method called ‘empty!’ on the @cart object.

It’s a convention in ruby that methods that modify an object in place
end in ‘!’ and methods that return a boolean end in ‘?’.

And does this:

redirect_to(:action => ‘index’)

No. This sends a 302 redirect to the browser so that it then requests
the index action.

Cheers,

Pete Y.

3

Hi –

On Sun, 3 Dec 2006, Pete Y. wrote:

Simple. It calls the method called ‘empty!’ on the @cart object.

It’s a convention in ruby that methods that modify an object in place
end in ‘!’ and methods that return a boolean end in ‘?’.

That’s sort of a convention-within-a-convention. The basic convention
is that !-methods are “dangerous”, compared to their non-dangerous
counterparts. The “danger” can, but doesn’t have to, take the form of
modifying the receiver.

There are also lots of methods that change their receivers but don’t
end in !, such as Array#pop, Hash#delete, etc.

David

–
David A. Black | [email protected]
Author of “Ruby for Rails” [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB’s Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

4

On Nov 22, 2006, at 00:24 , Jake Barnes wrote:

What does

@cart.empty!

mean?

Basically, it calls the empty! method on @cart object. Without
knowing what class @cart is, it’s impossible to say anything about
what it actually does. However, judging by the name, I would guess it
empties the cart. The exclamation mark is a naming convention that
indicates that the object itself is being modified (as opposed to
returning a modified copy of the object).

And does this:

redirect_to(:action => ‘index’)

mean simply that the action index should be called?

Pretty much, but not exactly. It adds a redirect header to the
response, indicating that the connected client should initiate a new
request, this time for the url identified by :action => ‘index’.

–
Jakob S. - http://mentalized.net