--- const_defined?(name)

    ⥸塼 name ǻꤵ̾Ƥ
    ֤ޤname  Symbol ʸǻꤷޤ

    ѡ饹䥤󥯥롼ɤ⥸塼줿оݤˤ
    ʤޤ(Object 㳰
    )

        module Kernel
          FOO = 1
        end

        # Object  include ⥸塼ФƤ
        # true ֤
        p Object.const_defined? :FOO    # => true

        module Bar
          BAR = 1
        end
        class Object
          include Bar
        end
        # 桼Υ⥸塼ФƤƱ
        p Object.const_defined? :BAR    # => true

        class Baz
          include Bar
        end
        # ObjectʳǤϼȤåо
        p Baz.const_defined? :BAR       # => false

