[ruby-core:56675] Re: [ruby-trunk - Feature #8781] Use require_relative() instead of require() if possible

On Fri, Aug 16, 2013 at 09:35:04AM -0300, Rodrigo Rosenfeld Rosas wrote:
> Em 16-08-2013 03:24, Aaron Patterson escreveu:
> >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. :-)
> >
> 
> Since we were discussing the design perspective, you just
> demonstrated how the design of using require can become much worse
> than using require_relative. When you're reading code you can be
> sure where to look for the files being loaded as expected while when
> using require you will always have to check $LOAD_PATH to be sure.

Use $LOADED_FEATURES:

[aaron@higgins example]$ touch foo.rb
[aaron@higgins example]$ irb -I .
irb(main):001:0> x = $LOADED_FEATURES.dup; nil
=> nil
irb(main):002:0> require 'foo'
=> true
irb(main):003:0> $LOADED_FEATURES - x
=> ["/Users/aaron/git/example/foo.rb"]
irb(main):004:0>

> I don't really think using require to allow such hacks is a good
> enough reason to favor require instead of require_relative... After
> all, Ruby already allows you to override code by monkey patching.
> Why would you need to override a full file?

Simply requiring a file will execute code.  There are times (especially
in tests) where you do not want ANY of the code to be executed (maybe it
connects to a database, or network, etc).

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