從 Enumerator 看 Ruby 的迭代器

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

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WEB DEVELOPER GAME DEVELOPER ૵ ࣌ ݭ໵ @elct9620

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No content

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As a Ruby developer, We use #each every day

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BUT How it works?

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#iterator Photo by Joel Fulgencio on Unsplash

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

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

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#loop vs #while

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

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#enumerator Photo by Glenn Carstens-Peters on Unsplash

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[].each # => #

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Why we need Enumerator?

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

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Enumerator vs Enumerable

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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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#generator Photo by m0851 on Unsplash

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#to_enum vs Enumerator.new

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

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

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

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

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Why we need Yielder?

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

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

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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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#lazy Photo by Kate Stone Matheson on Unsplash

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It is hard to ﬁgure out it, but useful

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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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