Adding a directory to $LOAD_PATH (Ruby)

Question

The Ruby load path is very commonly seen written as $: , but just because it is short, does not make it better. If you prefer clarity to cleverness, or if brevity for its own sake makes you itchy, you needn't do it just because everyone else is. Say hello to ...

$LOAD_PATH

... and say goodbye to ...

# I don't quite understand what this is doing...
$:

I would say go with $:.unshift File.dirname(__FILE__) over the other one, simply because I've seen much more usage of it in code than the $LOAD_PATH one, and it's shorter too!

I'm not too fond on the 'quick-and-dirty' way. Anyone new to Ruby will be pondering what $:. is.

I find this more obvious.

libdir = File.dirname(__FILE__)
$LOAD_PATH.unshift(libdir) unless $LOAD_PATH.include?(libdir)

Or if I care about having the full path...

libdir = File.expand_path(File.dirname(__FILE__))
$LOAD_PATH.unshift(libdir) unless $LOAD_PATH.include?(libdir)

UPDATE 2009/09/10

As of late I've been doing the following:

$:.unshift(File.expand_path(File.dirname(__FILE__))) unless
    $:.include?(File.dirname(__FILE__)) || $:.include?(File.expand_path(File.dirname(__FILE__)))

I've seen it in a whole bunch of different ruby projects while browsing GitHub.

Seems to be the convention?

If you type script/console in your Rails project and enter $:, you'll get an array that includes all the directories needed to load Ruby. The take-away from this little exercise is that $: is an array. That being so, you can perform functions on it like prepending other directories with the unshift method or the << operator. As you implied in your statement $: and $LOAD_PATH are the same.

The disadvantage with doing it the quick and dirty way as you mentioned is this: if you already have the directory in your boot path, it will repeat itself.

Example:

I have a plugin I created called todo. My directory is structured like so:

/---vendor
  |
  |---/plugins
        |
        |---/todo
              |
              |---/lib
                    |
                    |---/app
                          |
                          |---/models
                          |---/controllers
              |
              |---/rails
                    |
                    |---init.rb

In the init.rb file I entered the following code:

## In vendor/plugins/todo/rails/init.rb
    %w{ models controllers models }.each do |dir|
      path = File.expand_path(File.join(File.dirname(__FILE__), '../lib', 'app', dir))
      $LOAD_PATH << path
      ActiveSupport::Dependencies.load_paths << path
      ActiveSupport::Dependencies.load_once_paths.delete(path)
    end 

Note how I tell the code block to perform the actions inside the block to the strings 'models', 'controllers', and 'models', where I repeat 'models'. (FYI, %w{ ... } is just another way to tell Ruby to hold an array of strings). When I run script/console, I type the following:

>> puts $:

And I type this so that it is easier to read the contents in the string. The output I get is:

...
...
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/models
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/controllers
./Users/Me/mySites/myRailsApp/vendor/plugins/todo/lib/app/models

As you can see, though this is as simple an example I could create while using a project I'm currently working on, if you're not careful the quick and dirty way will lead to repeated paths. The longer way will check for repeated paths and make sure they don't occur.

If you're an experienced Rails programmer, you probably have a very good idea of what you're doing and likely not make the mistake of repeating paths. If you're a newbie, I would go with the longer way until you understand really what you're doing.