# safer monkey patch

###### tags: `advanced ruby`

ruby class 裡的method會融合，不論何時new

class Human
  def initialize
  end
end

person = Human.new

# monkey patch
class Human
  def age 
    puts 'not young'
  end
end

person.age
# => not young

- 想做個時間單位換秒數
`2.hours`
`3.days`

2.class
# => Integer

class Integer
  def minutes
    60 * self
  end
  
  def hours
    60 * minutes
  end
  
  def days
    24 * hours
  end
end

puts 2.minutes
puts 3.hours

# => 120
# => 10800

- 會覆寫require來的methods：

require 'active_support/all'

class Integer
  def minutes
    60 * self
  end
  
  def hours
    60 * minutes
  end
  
  def days
    24 * hours
  end
end

puts 3.hours.ago
# => undefined method `ago' for 10800:Integer (NoMethodError)

puts 3.hours.class
# => Integer

如何避免：

- `refine`定義monkey patch
- `using` 引入

# 使用refine避免大範圍污染同名methods
# refine必須包在module內

require 'active_support/all'
module GetSeconds
    refine Integer do 
        def minutes
            60 * self
        end
        def hours
            60 * minutes
        end
        def days
            24 * hours
        end
    end
end

puts 3.hours.class
# => ActiveSupport::Duration

# 用using引入refine 
# 僅有使用using的class才會被monkey patch
class MyPatch
    using GetSeconds
    
    def demo
        3.hours
    end
end

my_patch = MyPatch.new

puts my_patch.demo
# => 10800
puts my_patch.demo.class
# => Integer

- 原則上避免monkey patch
- 若要monkey patch，請使用`refine`，並用`using`引入

ref:
[Refinements](https://docs.ruby-lang.org/en/2.4.0/syntax/refinements_rdoc.html)