Should one use dashes or underscores when naming a gem with more than one word?

I'm confused about what the gem naming convention is when the gem name has more than one word.

• thinking-sphinx is the name of the gem, but the base *.rb file for this gem is lib/thinking_sphinx.rb (underscores)

• acts-as-taggable-on is the name of the gem, and the base *.rb file is called lib/acts-as-taggable-on.rb (hyphens)

• factory_girl uses an underscore in both the gem name and in the name of the base *.rb file

Does it matter if one uses underscores or hyphens? Is any emerging consensus here?

Eric Hodel has a blog post on this: A Project Naming Recommendation

> Rails solidified the convention of > mapping CamelCase class names to > underscored file names (class > IMAPProcesor is defined in > imap_processor.rb). Using underscored > gem names makes it easy for people to > figure out what file to require (same > as the project name) or what class > name to look for in ri. > > If I have a plugin gem or an extension > I’ll tack on the sub-project’s name > with a dash. If I wanted to add a new > handler for imap_to_rss for Chase bank > email, the gem would be named > imap_to_rss-chase.

Following the advice here, here is a table of how things would break down:

Gem name	Require statement	Main class or module
fancy_require	require 'fancy_require'	FancyRequire
ruby_parser	require 'ruby_parser'	RubyParser
net-http-persistent	require 'net/http/persistent'	Net::HTTP::Persistent
rdoc-data	require 'rdoc/data'	RDoc::Data
autotest-growl	require 'autotest/growl'	Autotest::Growl
net-http-digest_auth	require 'net/http/digest_auth'	Net::HTTP::DigestAuth