這只是一個簡單的問題，y.<<方法如何能夠停止代碼塊中間執行？

我希望代碼塊只運行一次，并且永遠不會在中間停止：/

e = Enumerator.new do |y|
    puts "Ruby"
    y << 1
    y << 2
    puts "Ruby"
    y << 3
end

puts e.each.next
puts e.each.next
puts e.each.next
e.rewind
puts e.each.next
puts e.each.next
puts e.each.next

uj5u.com熱心網友回復：

幾乎所有 Ruby 實作都是自由軟體和開源的，因此您只需查看源代碼即可了解它是如何實作的。

在Rubinius中，最有趣的部分是Enumerator::Iterator#reset，實作于core/enumerator.rb：

@fiber = Fiber.new stack_size: STACK_SIZE do
  obj = @object
  @result = obj.each { |*val| Fiber.yield *val }
  @done = true
end

和Enumerator::Iterator#next：

val = @fiber.resume

TruffleRuby的實作非常相似，如下所示src/main/ruby/truffleruby/core/enumerator.rb：

class FiberGenerator
  # irrelevant methods omitted

  def next
    reset unless @fiber

    val = @fiber.resume

    raise StopIteration, 'iteration has ended' if @done

    val
  end

  def reset
    @done = false
    @fiber = Fiber.new do
      obj = @object
      @result = obj.each do |*val|
        Fiber.yield(*val)
      end
      @done = true
    end
  end
end

JRuby也非常相似，您可以在以下代碼中看到core/src/main/ruby/jruby/kernel/enumerator.rb：

class FiberGenerator
  # irrelevant methods omitted

  def next
    reset unless @fiber&.__alive__

    val = @fiber.resume

    raise StopIteration, 'iteration has ended' if @state.done

    val
  end

  def reset
    @state.done = false
    @state.result = nil
    @fiber = Fiber.new(&@state)
  end

end

MRuby的實作非常相似，如您在mrbgems/mruby-enumerator/mrblib/enumerator.rb.

YARV也使用 Fibers，如 中所示enumerator.c，例如這里：

static void
next_init(VALUE obj, struct enumerator *e)
{
    VALUE curr = rb_fiber_current();
    e->dst = curr;
    e->fib = rb_fiber_new(next_i, obj);
    e->lookahead = Qundef;
}

static VALUE
get_next_values(VALUE obj, struct enumerator *e)
{
    VALUE curr, vs;

    if (e->stop_exc)
    rb_exc_raise(e->stop_exc);

    curr = rb_fiber_current();

    if (!e->fib || !rb_fiber_alive_p(e->fib)) {
    next_init(obj, e);
    }

    vs = rb_fiber_resume(e->fib, 1, &curr);
    if (e->stop_exc) {
    e->fib = 0;
    e->dst = Qnil;
    e->lookahead = Qundef;
    e->feedvalue = Qundef;
    rb_exc_raise(e->stop_exc);
    }
    return vs;
}

因此，毫不奇怪，在許多 Ruby 實作中Enumerator使用s 來實作。本質上只是 Ruby 對semi-coroutines的稱呼，當然，coroutines 是一種流行的實作生成器和迭代器的方式。例如，CPython 和 CoreCLR 也使用協程實作生成器。FiberFiber

One exception to this seems to be Opal. My assumption was that Opal would use ECMAScript Generators to implement Ruby Enumerators, but it does not look like that is the case. The implementation of Ruby Enumerators in Opal is found in opal/corelib/enumerator.rb, opal/corelib/enumerator/generator.rb, and opal/corelib/enumerator/yielder.rb with some help from opal/corelib/runtime.js, but unfortunately, I don't fully understand it. It does not appear to use either Ruby Fibers or ECMAScript Generators, though.

By the way, your usage of Enumerators is somewhat strange: you call Enumerator#each six times without a block, but calling Enumerator#each without a block just returns the Enumerator itself:

each → enum

Iterates over the block according to how this Enumerator was constructed. If no block and no arguments are given, returns self.

So, in other words, all those calls to Enumerator#each are just no-ops. It would make much more sense to just call Enumerator#next directly:

puts e.next
puts e.next
puts e.next
e.rewind
puts e.next
puts e.next
puts e.next

標籤：红宝石 枚举器

上一篇：用于銀行交易決議的正則運算式

下一篇：如何使用ruby??僅從json物件中迭代和檢索值