Catching Errors in Ruby

I have a statement that looks something like this

if not @user.verified? or @user.credit_card.expired?
  # do stuff
end

The problem is the ca开发者_StackOverflowse where the @user does not yet have a credit card because expired? will raise an exception because of the nil value.

Is there a succinct way to catch the error inline without having to resort to extra if statements?

To avoid this exception you can use Rails 2.3/3 built-in method: try

if not @user.verified? or @user.credit_card.try(:expired?)
  # do stuff
end

The andand gem allows for a guarded method invocation if and only if the object is not null.

Your code snippet would look like this:

if not @user.verified? or @user.credit_card.andand.expired?
  # do stuff
end

You can install it with gem install andand and you're good to go.

Website: http://andand.rubyforge.org/

The code

@user.credit_card.expired?

Would be called a violation of the Law of Demeter. That law states you're allowed to call any method you like on @user, but not on @user.credit_card.