A function for inquiring if a library is available. Automatically requires the library if it is available.

create_has_library.rb

    # Create a method `has_<library>?` on Module that requires the library and
    # return a boolean indicating if the library is available.
    #
    # @param library [String] The library name.
    # @return [Boolean] Whether the library is available or not.
    def create_has_library(library) #:nodoc:
      define_singleton_method("has_#{library}?") do
        cv = "@@#{library}"
        unless class_variable_defined? cv
          begin
            require library.to_s
            class_variable_set(cv, true)
          rescue LoadError
            class_variable_set(cv, false)
          end
        end
        class_variable_get(cv)
      end
    end
  end