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Micah's General Guidelines on Ruby require

by: micah | October 8th, 2007 |

Ruby files have to require other files. There’s not avoiding it. Techniques to manage require statements are numerous and varied. Having tried most of them, I’ve found a system that works well for me. What follows are the guidelines I use to manage Ruby require statements.

1. Establish a Convenient Search Path

Although it’s possible to use absolute paths or complex relative paths such as below,

1. require "/Users/micahmartin/Projects/ttt/lib/game"
2. require File.dirname(__FILE__) + "../../../lib/ai/winner"

this should be avoided as much as possible. Otherwise you’ll be fixing dozens of require statements every time you move a file. It’s no fun. You’ll want your requires to look like this:

1. require "game"
2. require "ai/winner"

To achieve this, add your lib directory to the ruby search path.

$: << File.expand_path(File.dirname(FILE) + “/../lib”))

This will have to go in one of the first files that gets loaded. If you’ve got a standalone Ruby app, you could add this to the startup script. In a Rails app, it can go in environment.rb. If you’re using RSpec, you may want to add it to spec_helper.rb.

2. Independent Requiring over Require Farms

In some projects, you’ll find files that contain nothing but require statements. It’s common in gem projects. The advantage is that users of the library need only require one file which in turn requires everything else you’ll need. Convenient huh? Sure is. But there are 2 major consequences of this:

1. Maintenance Mayhem - Every time you add, delete, or rename a file you have to remember to update the require farm file. It’s easy to forget. And the order of requires can get very hard to manage especially if you end up with cyclic dependancies.
2. Drowning in Dependancies - Require Farms have a tendency to require more than you want. If there’s only a portion of the library you’d like to use, with the Require Farm you get the whole thing. The extra dependancies will consume more memory at run time and they may add undesired behavior to your system. In general, this is a violation of the Dependancy Inversion Principle.

Rather than build Require Farms, allow each file to be responsible for it’s own dependancies. Let each file require the files it needs to work. This approach can be a bit annoying as you’ll find your self using altogether more require statements, but it’ll pay off in the long run. With each file independently managing it’s dependancies, the system will be easier to maintain and it’s components more reusable.

3. Building Absolute Paths

Try as you may, you can’t always avoid using absolute file paths in your require statements. The following is reliable way to refer to other files.

1. File.join(File.expand_path(File.dirname(__FILE__)), "..", "spec_helper")

Let me break it down. First:

1. File.dirname(__FILE__)

This gives you the directory of the current file that is being executed. However, you never know what you’re gonna get since the form of the path is based on how the program was executed. This might give you an absolute path or it might give you a relative path from anywhere on the system. In some cases, Ruby won’t do what you expect with relative paths so it’s best to expand this into an absolute path.

1. File.expand_path(File.dirname(__FILE__)

Now you’ve got an absolute file path and you just have to add a relative path to the desired file. Normally I’d do this:

1. File.expand_path(File.dirname(__FILE__) + "../spec_helper")

However, this is not quite portable since I’m using forward slashes. To get this to work on any system independent of file separator, use File.join as shown above. Use this technique to require files when you don’t have your search path configured.

Happy Requiring!

14 Responses to “Micah's General Guidelines on Ruby require”

1. w0 Says:
   October 18th, 2008 at 06:32 PM fine little stuff always helps. thanks !
2. mamboze Says:
   October 18th, 2008 at 06:32 PM thanks from a ruby noob for the very useful information
3. wyderp Says:
   October 18th, 2008 at 06:32 PM a thorough explanation, which is rare. you're right, the cyclic dependency issue is non-trivial. compilers need to be expanded to handle cyclic refs, redundancy, ordering, etc. just like installation software has done for years (and screwed up for years i might add).
4. Eric Anderson Says:
   October 18th, 2008 at 06:32 PM Correct me if I am wrong but I believe ruby will use either a forward slash or a backslash regardless of operating system. So the File.join is not strictly necessary to make it cross platform.
5. Steve Says:
   October 18th, 2008 at 06:32 PM Let's just all agree that the default is "Correct me if I am wrong", so there would be no need to preface statements with this kind of qualifier unless you mean "Do NOT correct me if I am wrong". Wouldn't that save a lot of wasted bandwidth? Trust me - if you are wrong, someone will correct you. You don't have to give permission.
6. Antobot Says:
   October 18th, 2008 at 06:32 PM Steve: As far as I can tell you are correct though feel free to correct me if I am wrong. Eric Anderson: ri File.join
7. Adrian Says:
   October 18th, 2008 at 06:32 PM Thanks for the post, it helped a lot.
8. snash Says:
   November 22nd, 2008 at 04:21 PM

   $: << File.expand_path(File.dirname(FILE) + “/../lib”))

   should read

   $: << File.expand_path(File.dirname(FILE) + “/../lib”))

   no?

9. Ari Says:
   January 16th, 2009 at 05:50 PM

   Thanks for this! As unglamorous as it is, it is very important, and yet I couldn't find this basic info on how to properly structure my load paths anywhere! Thanks!

10. Luke Says:
    January 20th, 2009 at 04:25 AM

    @snash, sadly your correct fell at the same hurdle as the original example. To avoid falling at it too, I think what you're trying to say is that there should be a double underscore before and after the word 'FILE'.

11. Caitlin - Madrid Reservation Says:
    February 15th, 2009 at 07:19 AM

    thank you for giving us these advices. I will use them in my work. You're right, the cyclic dependency issue is non-trivial. compilers need to be expanded to handle cyclic refs, redundancy, ordering, etc. just like installation software has done for years (and screwed up for years i might add).

12. Jacques Says:
    March 7th, 2009 at 03:34 PM

    Thanks mate! Exactly what I needed.

13. obligatory grammar corrector Says:
    August 13th, 2009 at 12:46 AM

    "Rather than build Require Farms, allow each file to be responsible for it’s own dependancies. Let each file require the files it needs to work. This approach can be a bit annoying as you’ll find your self using altogether more require statements, but it’ll pay off in the long run. With each file independently managing it’s dependancies, the system will be easier to maintain and it’s components more reusable."

    All of the above "it's" should be "its".

14. Ragmaanir Says:
    November 28th, 2009 at 03:17 PM

    shouldn't it be "dependEncy" instead of "dependAncy"?

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