e = [1,2,3].map
p e.next           #=> 1
e.Feed "a"
p e.next           #=> 2
e.Feed "b"
p e.next           #=> 3
e.Feed "c"
begin
  e.next
rescue StopIteration
  p $!.result      #=> ["a","b","c"]
end

但是当我通过Enumerator.new创建枚举时呢？

# a naive rework of the above enum
e2 = Enumerator.new do |y|
  [1,3].each do |x|
    y << x
  end
  # raise StopIteration,FED # <= how to get `FED`?
end

p e2.next           #=> 1
e2.Feed "a"
p e2.next           #=> 2
e2.Feed "b"
p e2.next           #=> 3
e2.Feed "c"
begin
  e2.next
rescue StopIteration
  p $!.result      #=> nil
end

我如何修改它以匹配API？

我尝试过的事情：

e2 = Enumerator.new do |y|
  [1,3].each do |x|
    @fed = yield
    y << x
  end
  raise StopIteration,@fed
end

e2 = Enumerator.new do |y|
  [1,3].each do |x|
    y << yield(x)
  end
  raise StopIteration,y
end

e2 = Enumerator.new do |y|
  enum = [1,3].each{|x| yield x }.to_enum
  y << enum.next
  raise StopIteration,y
end

有趣的是,当第二次调用Feed时,它们都会产生相同的错误：

# Ignoring all the other errors that jump up…
p e2.next           #=> 1
e2.Feed "a"
# nil
p e2.next           #=> 2
e2.Feed "b"

TypeError: Feed value already set

TypeError：已设置的Feed值意味着它正在某处收集值,我只是不知道如何访问它.

#Feed的C源代码：

static VALUE
enumerator_Feed(VALUE obj,VALUE v)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->Feedvalue != Qundef) {
        rb_raise(rb_eTypeError,"Feed value already set");
    }
    e->Feedvalue = v;

    return Qnil;
}

所以Feedvalue是我的目标.我已经使用Pry进入了该方法的操作,但找不到与Feed或Feedvalue相关的方法或变量. Rubinius makes this available explicitly(至少作为实例变量).

我很难过.

任何帮助或见解将不胜感激.

解决方法

e = [1,3].map
=> #<Enumerator: [1,3]:map>

e2 = Enumerator.new do |y|
  [1,FED # <= how to get `FED`?
end
=> #<Enumerator: #<Enumerator::Generator:0x007fa69b056b50>:each>

[1,3].to_enum(:map)
=> #<Enumerator: [1,3]:map>

Enumerator.new([1,3],:map)

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