# File lib/chef/resource_collection.rb, line 104
    def lookup(resource)
      lookup_by = nil
      if resource.kind_of?(Chef::Resource)
        lookup_by = resource.to_s
      elsif resource.kind_of?(String)
        lookup_by = resource
      else
        raise ArgumentError, "Must pass a Chef::Resource or String to lookup"
      end
      res = @resources_by_name[lookup_by]
      unless res
        raise Chef::Exceptions::ResourceNotFound, "Cannot find a resource matching #{lookup_by} (did you define it first?)"
      end
      @resources[res]
    end