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
2. WEB DEVELOPER GAME DEVELOPER ૵ ࣌ ݭ໵ @elct9620
4. As a Ruby developer, We use #each every day
5. BUT How it works?
6. #iterator Photo by Joel Fulgencio on Unsplash
7. def iterator(&block) yield 1 yield 2 yield 3 end
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
9. def each(&block) @i = 0 yield @i += 1 until @i >= 10 end
10. #loop vs #while
11. static VALUE loop_i(void) { for (;;) { rb_yield_0(0, 0); } return Qnil; } Loop is a method with a block
12. #enumerator Photo by Glenn Carstens-Peters on Unsplash
13. [].each # => #<Enumerator: []:each>
14. Why we need Enumerator?
15. enum = [1, 2, 3].to_enum enum.next # => 1 enum.next # => 2 enum.next # => 3
16. Enumerator vs Enumerable
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 {}
18. #generator Photo by m0851 on Unsplash
19. #to_enum vs Enumerator.new
20. class List def each(&block) #... end end List.new.to_enum # => #<Enumerator: #<List:0x00007fa490988a78>:each>
21. class List def pop(&block) #... end end List.new.to_enum(:pop) # => #<Enumerator: #<List:0x00007fa491081fa0>:pop>
22. If Enumerator.new didn t have target ruby will create a Generator
23. Enumerator.new do |yielder| yielder << 1 yielder << 2 end
24. Why we need Yielder?
25. enum = Enumerator.new do yield 1 yield 2 end puts enum.to_a # => no block given (yield) (LocalJumpError)
26. class Yielder def initialize(&block) @proc = block.to_proc end def <<(value) @proc.call(value) self end end
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
28. #lazy Photo by Kate Stone Matheson on Unsplash
29. It is hard to figure out it, but useful
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
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
32. backpack.map(&:rect).take(1).to_a # => 1 # => 2 # => 3 backpack.lazy.map(&:rect).take(1).to_a # => 1
33. backpack.take(1).to_a # => 1 backpack.lazy.take(1).to_a # => 1
34. backpack = Backpack.new.to_enum backpack.lazy.reverse_each.take(1).to_a # => 1 # => 2 # => 3
35. And last, let s discuss implement #lazy in Ruby
36. Thanks