定义单例方法的方式

singleton_methods.rb

# 定义单例方法的方式

# 1
class A
  def self.hi
    p 'hi'
  end
end

# 2
class A
  class << self
    def hello
      p 'hello'
    end
  end
end

# 3
def A.hey
  p 'hey'
end

# 4
(class << A; self; end).class_eval do
  def you
    p 'you'
  end
end

# 5
A.singleton_class.class_eval do
  def folk
    p 'folk'
  end
end

A.hi
A.hello
A.hey
A.you
A.folk
p A.singleton_methods