instance method specification

# File railties/lib/rails/gem_dependency.rb, line 100
    def specification
      # code repeated from Gem.activate. Find a matching spec, or the currently loaded version.
      # error out if loaded version and requested version are incompatible.
      @spec ||= begin
        matches = Gem.source_index.search(self)
        matches << @@framework_gems[name] if framework_gem?
        if Gem.loaded_specs[name] then
          # This gem is already loaded.  If the currently loaded gem is not in the
          # list of candidate gems, then we have a version conflict.
          existing_spec = Gem.loaded_specs[name]
          unless matches.any? { |spec| spec.version == existing_spec.version } then
            raise Gem::Exception,
                  "can't activate #{@dep}, already activated #{existing_spec.full_name}"
          end
          # we're stuck with it, so change to match
          version_requirements = Gem::Requirement.create("=#{existing_spec.version}")
          existing_spec
        else
          # new load
          matches.last
        end
      end
    end