# File lib/rubygems.rb, line 350
  def self.available?(gem, *requirements)
    requirements = Gem::Requirement.default if requirements.empty?

    unless gem.respond_to?(:name) and
           gem.respond_to?(:version_requirements) then
      gem = Gem::Dependency.new gem, requirements
    end

    !Gem.source_index.search(gem).empty?
  end