available?

# File lib/rubygems.rb, line 278
  def self.available?(dep, *requirements)
    requirements = Gem::Requirement.default if requirements.empty?

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

    not dep.matching_specs(true).empty?
  end