從 Enumerator 看 Ruby 的迭代器

RubyConf TW 2019

Transcript

1. Review Ruby s Iterator
   with Enumerator
   Photo by Tine Ivanič on Unsplash
   

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2. WEB DEVELOPER
   GAME DEVELOPER
   ૵
   ࣌
   ݭ໵
   @elct9620
   

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4. As a Ruby developer,
   We use #each every day
   

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5. BUT
   How it works?
   

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6. #iterator
   Photo by Joel Fulgencio on Unsplash
   

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7. def iterator(&block)
   yield 1
   yield 2
   yield 3
   end
   

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8. VALUE
   rb_block_call(VALUE obj, ID mid, int argc, const VALUE * argv,
   VALUE (*bl_proc) (ANYARGS), VALUE data2)
   {
   struct iter_method_arg arg;
   arg.obj = obj;
   arg.mid = mid;
   arg.argc = argc;
   arg.argv = argv;
   return rb_iterate(iterate_method, (VALUE)&arg, bl_proc, data2);
   }
   The block call is iterate in ruby
   

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9. def each(&block)
   @i = 0
   yield @i += 1 until @i >= 10
   end
   

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10. #loop
    vs
    #while
    

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11. static VALUE
    loop_i(void)
    {
    for (;;) {
    rb_yield_0(0, 0);
    }
    return Qnil;
    }
    Loop is a method with a block
    

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12. #enumerator
    Photo by Glenn Carstens-Peters on Unsplash
    

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13. [].each
    # => #
    

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14. Why we need Enumerator?
    

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15. enum = [1, 2, 3].to_enum
    enum.next
    # => 1
    enum.next
    # => 2
    enum.next
    # => 3
    

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16. Enumerator
    vs
    Enumerable
    

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17. class Backpack
    include Enumerable
    def initialize(items)
    @items = items
    end
    def each(&block)
    @items.each(&block)
    end
    end
    backpack = Backpack.new([:water, :apple])
    backpack.map {}
    

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18. #generator
    Photo by m0851 on Unsplash
    

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19. #to_enum
    vs
    Enumerator.new
    

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20. class List
    def each(&block)
    #...
    end
    end
    List.new.to_enum
    # => #:each>
    

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21. class List
    def pop(&block)
    #...
    end
    end
    List.new.to_enum(:pop)
    # => #:pop>
    

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22. If Enumerator.new didn t have target
    ruby will create a Generator
    

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23. Enumerator.new do |yielder|
    yielder << 1
    yielder << 2
    end
    

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24. Why we need Yielder?
    

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25. enum = Enumerator.new do
    yield 1
    yield 2
    end
    puts enum.to_a
    # => no block given (yield) (LocalJumpError)
    

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26. class Yielder
    def initialize(&block)
    @proc = block.to_proc
    end
    def <<(value)
    @proc.call(value)
    self
    end
    end
    

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27. class Generator
    def initialize(&block)
    @proc = block.to_proc
    end
    def each(&_block)
    yielder = Yielder.new { |x| yield x }
    @proc.call(yielder)
    end
    end
    

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28. #lazy
    Photo by Kate Stone Matheson on Unsplash
    

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29. It is hard to figure out it, but useful
    

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30. class Backpack
    def each(&block)
    yield p(1)
    yield p(2)
    yield p(3)
    end
    end
    backpack = Backpack.new.to_enum
    backpack.map(&:rect).take(1).to_a
    backpack.lazy.map(&:rect).take(1).to_a
    

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31. class Backpack
    def each(&block)
    yield p(1)
    yield p(2)
    yield p(3)
    end
    end
    backpack = Backpack.new.to_enum
    backpack.map(&:rect).take(1).to_a
    backpack.lazy.map(&:rect).take(1).to_a
    

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32. backpack.map(&:rect).take(1).to_a
    # => 1
    # => 2
    # => 3
    backpack.lazy.map(&:rect).take(1).to_a
    # => 1
    

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33. backpack.take(1).to_a
    # => 1
    backpack.lazy.take(1).to_a
    # => 1
    

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34. backpack = Backpack.new.to_enum
    backpack.lazy.reverse_each.take(1).to_a
    # => 1
    # => 2
    # => 3
    

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35. And last,
    let s discuss implement #lazy in Ruby
    

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36. Thanks
    

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