From: Aaron Patterson <tenderlove@...>
Date: 2013-08-16T15:24:43+09:00
Subject: [ruby-core:56643] Re: [ruby-trunk - Feature #8781] Use require_relative() instead of require() if possible

On Fri, Aug 16, 2013 at 03:00:59PM +0900, SASADA Koichi wrote:
> (2013/08/16 14:21), Aaron Patterson wrote:
> > If you move the file, then all calls to `require_relative` in that file
> > must be changed.  If you had just used `require`, the file can be moved
> > without changes.
> 
> Which case?
> 
> For example, there are files:
>   foo.rb
>   foo/bar/a.rb
> 
> And foo.rb has "require 'foo/bar/a'".
> 
> If you move foo/bar/a.rb to foo/bar/b.rb, then you need to rewrite to
> "require 'foo/bar/b'".
> 
> If you move foo/bar/a.rb to foo/baz/a.rb, then you need to rewrite to
> "require 'foo/baz/a'".

Yes, you changed the files that *depend on* the source for 'foo/bar/a',
but 'foo/bar/a.rb' itself did not change.

If something *you depend on* changes location, then yes, you should
change your code.

Here is an example with require_relative:

$ mkdir -p lib/foo/bar
$ touch lib/foo.rb
$ echo "require_relative '../../foo'" > lib/foo/bar/baz.rb
$ ruby -I lib -r'foo/bar/baz' -e 0
$ mv lib/foo/bar/baz.rb lib/foo/
$ ruby -I lib -r'foo/baz' -e 0
/Users/aaron/git/example/lib/foo/baz.rb:1:in `require_relative': cannot load such file -- /Users/aaron/git/example/foo (LoadError)
        from /Users/aaron/git/example/lib/foo/baz.rb:1:in `<top (required)>'
        from /Users/aaron/.rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
        from /Users/aaron/.rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
$ 

In the above example, "foo.rb" did not change location, yet I have to
change the call to `require_relative`.

foo/bar/baz.rb depends on foo.rb.  foo.rb did not change locations, so
why do I have to change my code?

Let's take the same example, "foo/bar/baz.rb" that depends on "foo.rb",
but instead use `require`:

$ mkdir -p lib/foo/bar
$ echo "require 'foo'" > lib/foo/bar/baz.rb
$ touch lib/foo.rb
$ ruby -I lib -r'foo/bar/baz' -e 0
$ mv lib/foo/bar/baz.rb lib/foo/
$ ruby -I lib -r'foo/baz' -e 0
$

My dependency, "foo.rb", did not change locations, so I don't need to
change my code.  "foo/bar/baz.rb" works as-is, no matter where it is on
the filesystem. :-)

-- 
Aaron Patterson
http://tenderlovemaking.com/