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Question

Rubygems. A newly installed gem isn't added to $LOAD_PATH ($:)

Answer 1

+1 A:

You haven't loaded any gems yet:

ruby -e '
  puts "Before require: #{$:.grep /rack/}"
  require "rack"
  puts "After require: #{$:.grep /rack/}"
'
# Before require: []
# After require: ["C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/bin", 
#                 "C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/lib"]

ruby -e '
  puts "Before gem: #{$:.grep /rack/}"
  gem "rack"
  puts "After gem: #{$:.grep /rack/}"
  require "rack"
  puts "After require: #{$:.grep /rack/}"
'
# Before gem: []

# After gem: ["C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/bin", 
#             "C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/lib"]
# After require: ["C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/bin", 
#                 "C:/Ruby/YARV/1.9.2/lib/ruby/gems/1.9.1/gems/rack-1.2.1/lib"]

Jörg W Mittag 2010-09-06 00:27:50

I can't require it because it isn't in $:. Look at the updates above.

Shamaoke 2010-09-06 01:08:37

As you can clearly see from the code I posted, it isn't in my load path, either, and yet I *can* require it. Gems only get added to the load path *after* they have been required. (Or more precisely, after they have been *activated*, which `require` does automatically for you.) I have added a fourth and fifth example, which makes this even more obvious.

Jörg W Mittag 2010-09-06 02:18:38

I don't know why but it works now. However for the `require` method only. The `load` method still raises **LoadError**. Don't know why Rubygems has so wierd behaviour. As for loading mechanism yes you was right it works exactly as you wrote. Thanks for the explanations.

Shamaoke 2010-09-06 03:08:02

@Shamaoke: RubyGems overrides the `require` method so that when a file is not found in the load path, it looks through all the gems, and when it finds the file there, it activates the gem, adds it to the load path and retries the `require`. It does, however, not patch the `load` method.

Jörg W Mittag 2010-09-06 03:10:52

So, the only way to `load` a gem is manually adding its directory to the load path and then actually load the file, isn't it?

Shamaoke 2010-09-06 03:40:24

@Shamaoke: As you can see in my second example above, once you activate the gem, it is added to the load path. There is no need to do that manually.

Jörg W Mittag 2010-09-06 03:52:25

Answer 2

A:

things have changed for 1.9.2

http://wiki.github.com/rdp/ruby_tutorials_core/ruby-talk-faq#gem_loading_fails_191

it basically auto loads rubygems for you now, instead of pre-populating the load path.

rogerdpack 2010-09-07 17:02:44

Thanks for clarification, **rogerdpack**. Now I understand the difference in the gem loading mechanismes between the current Rubygem version and the previous ones.

Shamaoke 2010-09-08 02:06:26

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Rubygems. A newly installed gem isn't added to $LOAD_PATH ($:)

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