动态定义ruby子类，和判断是否定义

上篇有个标准的定义动态类变量

class MyClass
  class << self
    attr_accessor :my_constant
  end
  def my_method
    self.class.my_constant = "blah"
  end
end

p MyClass.my_constant #=> nil
MyClass.new.my_method

p MyClass.my_constant #=> "blah"

如果类也动态定义，那么子类和module怎么定义进去的

dynamic_name = "TestEval2"

Object.const_set(dynamic_name, Class.new{def method1() 42 end }})
dummy2 = eval("#{dynamic_name}")
puts "dummy2: #{dummy2}"

dynamic_name = "SubTestEval2"

SubModule.const_set(dynamic_name, Class.new(TestEval2){def method1() 43 end })
dummy3 = eval("#{dynamic_name}")
puts "dummy3: #{dummy3}"

判断动态类是否存在

def class_exists?(class_name)
  eval("defined?(#{class_name}) && #{class_name}.is_a?(Class)") == true
end

class_name = "Blorp"
class_exists?(class_name)
=> false

class_name = "String"
class_exists?(class_name)
=> true

define_method定义的方法参数放到哪？

define_method(:say_hi) { |other| puts "Hi, " + other }