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Ruby - Dry Your Code With Tap

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Yields self to the block, and then returns self. The primary purpose of this method is to “tap into” a method chain, in order to perform operations on intermediate results within the chain.

在 ruby 中，因為太過方便很常會用到 method chain，透過 tap 可以變得更 dry

實際上就是，透過 yield 將 block 帶過去，再透過 self 將自身帶回來

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# activesupport/lib/active_support/core_ext/object/misc.rb, line 53
def tap
  yield self
  self
end

另一個用處，便於檢查 method chain 裡的 info

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(1..10)
  .tap {|x| puts "original: #{x.inspect}"}
  .to_a.tap {|x| puts "array: #{x.inspect}"}
  .select {|x| x%2==0}.tap {|x| puts "evens: #{x.inspect}"}
  .map { |x| x*x }.tap {|x| puts "squares: #{x.inspect}"}

# original: 1..10
# array: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
# evens: [2, 4, 6, 8, 10]
# squares: [4, 16, 36, 64, 100]

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class Dog
  attr_accessor :name

  def self.create_instance
    dog = new
    dog.name = "hey"
    dog
  end
end

dog = Dog.create_instance
dog.name

透過 tap 改成

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class Dog
  attr_accessor :name

  def self.create_instance
    Dog.new.tap do |dog|
      dog.name = "hey"
    end
  end
end

dog = Dog.create_instance
dog.name

參考文件

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