Ruby require

Detlef_R · May 1, 2014, 12:42pm

Got a Question to $LOAD_PATH.

When using require ‘mygem’ in the ruby documentation is written:

“If the filename does not resolve to an absolute path, it will be
searched for in the directories listed in $LOAD_PATH”

But when i output the $LOAD_PATH before the require statement on mri
2.1.1 i got following:

/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby/2.1.0/x86_64-linux
/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby/2.1.0/x86_64-linux
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby
/home/benny/.rubies/mri-2.1.1/lib/ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/2.1.0/x86_64-linux

After the require statment for example i wanna use stackprof the
$LOAD_PATH is:

/home/benny/.gem/ruby/2.1.1/extensions/x86_64-linux/2.1.0-static/stackprof-0.2.6
/home/benny/.gem/ruby/2.1.1/gems/stackprof-0.2.6/lib
/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby/2.1.0/x86_64-linux
/home/benny/.rubies/mri-2.1.1/lib/ruby/site_ruby
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby/2.1.0/x86_64-linux
/home/benny/.rubies/mri-2.1.1/lib/ruby/vendor_ruby
/home/benny/.rubies/mri-2.1.1/lib/ruby/2.1.0
/home/benny/.rubies/mri-2.1.1/lib/ruby/2.1.0/x86_64-linux

This is kinda weird for me because in the documentation there is said a
require statement tries to load a library from the $LOAD_PATH when it’s
not a absolute path and doesn’t modify it?

Is there anything else going on?
Maybe rubygems itself just includes gems to the load path if they are
required explicitly?

kuzb · May 1, 2014, 11:32pm

Adding the lib directory of a required gem to $LOAD_PATH is documented
by rubygems:

=====
Loading code

At its core, RubyGems exists to help you manage Ruby’s $LOAD_PATH, which
is how the require statement picks up new code. There’s several things
you can do to make sure you’re loading code the right way.

…
…

Mangling the load path

Gems should not change the $LOAD_PATH variable. RubyGems manages this
for you. Code like this should not be necessary:

lp = File.expand_path(File.dirname(FILE))
unless $LOAD_PATH.include?(lp)
$LOAD_PATH.unshift(lp)
end

Or:

DIR = File.dirname(FILE)

$LOAD_PATH.unshift DIR unless
$LOAD_PATH.include?(DIR) ||
$LOAD_PATH.include?(File.expand_path(DIR))

When RubyGems activates a gem, it adds your package’s lib folder to the
$LOAD_PATH ready to be required normally by another lib or application.
It is safe to assume you can then require any file in your lib folder.

kuzb · May 2, 2014, 12:15am

Found the interesting part for me:

github.com

rubygems/rubygems/blob/master/lib/rubygems/core_ext/kernel_require.rb#L38https://github.com/rubygems/rubygems/blob/master/lib/rubygems/core_ext/kernel_require.rb#L38


      
          #   is.
          # * Otherwise, installed gems are searched for a file that matches.
          #   If it's found in gem 'y', that gem is activated (added to the
          #   loadpath).
          #
          # The normal <tt>require</tt> functionality of returning false if
          # that file has already been loaded is preserved.
          
          
def require(path) # :doc:
            return gem_original_require(path) unless Gem.discover_gems_on_require
          
          
  begin
              RUBYGEMS_ACTIVATION_MONITOR.enter
          
          
    path = path.to_path if path.respond_to? :to_path
          
          
    if spec = Gem.find_unresolved_default_spec(path)
                # Ensure -I beats a default gem
                resolved_path = begin
                  rp = nil
                  load_path_check_index = Gem.load_path_insert_index - Gem.activated_gem_paths

Just if anyone needs this too

kuzb · May 2, 2014, 12:06am

okay thx to clear this up
just wondered how the $LOAD_PATH got modified by requiring a gem

i’ll dig into the rubygems source to make it more clearer to me

Ruby require

When RubyGems activates a gem, it adds your package’s lib folder to the $LOAD_PATH ready to be required normally by another lib or application. It is safe to assume you can then require any file in your lib folder.

When RubyGems activates a gem, it adds your package’s lib folder to the
$LOAD_PATH ready to be required normally by another lib or application.
It is safe to assume you can then require any file in your lib folder.