[philwelch]

It's an imported Perlism, back from the days of the old assert idiom `foo == bar or die`.

If `foo == bar` evaluates to true, the `or` is short-circuited, else it calls the built-in `die` function which kills the process.

[lloeki]

More precisely && and || are meant to stand in boolean tests, whereas and and or are meant to tie expressions together DSL style, as an alternative to if/then, like so:

   @current_user.logged_in? or redirect_to login_path
   @current_user.can? :do_this or render :status => 403
   shirt.blue? and return bar
   put_suit_on or put_pants_on

[graywh]

That's a good example

  shirt.blue? and return bar

would be equivalent to

  return bar if shirt.blue?

You can do the same with or and unless.

[philwelch]

I find the postfix if and unless far more readable than the Perlish and and or operators. The "or die" construction for asserts is really amusing though.