From: Magnus Holm <judofyr@...>
Date: 2011-01-21T06:40:46+09:00
Subject: [ruby-core:34686] Re: Returning from the callee

On Thu, Jan 20, 2011 at 22:25, Rodrigo Rosenfeld Rosas
<rr.rosas@gmail.com> wrote:
> What I really want is a simple way for doing simple things. I usually use a
> one-line code for a simple statement like this because it makes easier for
> me for reading the code.
>
> If it was possible to write
>
> render text: 'failed' unless request.valid?
> ...
> render 'template/output'
>
> , why would I have to write things like the code below?
>
> unless request.valid?
> �� ��render text: 'failed' unless request.valid?
> �� ��return
> end
> ...
> render 'template/output
>
> I don't want to give focus on special case error handling but on the usual
> case instead.
>
> Currently, it is possible to write something like:
>
> return(render(text: 'invalid')) unless request.valid?

This is actually possible using catch/throw, and I believe `render` in
Rails worked like that in previous versions. Let me give you an
example from Camping:

  module Helpers
    # Redirects to login-page unless logged in
    def logged_in!
      unless @current_user
        redirect Login
        throw :halt
      end
    end
  end

  # Inside a controller:
  logged_in!
  render :index

Of course, this means that the callee actually have to add a
catch-clause. It's as simple as this:

  def service
    # before: response = run_controller
    # after:
    response = catch(:halt) { run_controller }
  end

Yes, this means that you'll have to explicitly choose how many
stackframes you want to "escape" from, but that actually makes it less
fragile. For instance, I could define another helper like this:

  module Helpers
    def admin!
      logged_in!
      unless @current_user.is_a?(Admin)
        redirect AccessDenied
        throw :halt
      end
    end
  end

If logged_in! used a "return callee" approach, this wouldn't have
worked because it would simply returned the admin!-method. If you use
catch/throw explicitly you get more control over what you're
*actually* trying to accomplish.