[英]Ruby Enumerator-based lazy flatten method
Michael Harrison has a great post on lazy enumerators in Ruby , providing an implementation of lazy_select
and lazy_map
.迈克尔·哈里森 (Michael Harrison) 在 Ruby 中发表了一篇关于惰性枚举器的精彩文章,提供了
lazy_select
和lazy_map
的实现。 I am wondering whether the following implementation of lazy_flatten
should have special processing for anything other than Enumerator
and Enumerable
types.我想知道下面的
lazy_flatten
实现是否应该对Enumerator
和Enumerable
类型以外的任何东西进行特殊处理。
class Enumerator
def lazy_flatten
Enumerator.new do |yielder|
self.each do |value|
if value.kind_of? Enumerator
value.lazy_flatten.each do |v|
yielder.yield v
end
elsif value.kind_of? Enumerable
value.flatten.each do |v|
yielder.yield v
end
else
yielder.yield value
end
end
end
end
end
flatten
beneath.flatten
。Enumerator
is Enumerable
, so I think you don't need to handle it separately. Enumerator
是Enumerable
,所以我认为你不需要单独处理它。lazy_flatten
to be method on Enumerable
.lazy_flatten
成为Enumerable
上的方法。 Here's how I would implement it:下面是我将如何实现它:
module Enumerable
def lazy_flatten
Enumerator.new do |yielder|
each do |element|
if element.is_a? Enumerable
element.lazy_flatten.each do |e|
yielder.yield(e)
end
else
yielder.yield(element)
end
end
end
end
end
Note that in Ruby 2.0+, you don't need to do this, you can just use Enumerable#lazy
, which returns an Enumerator::Lazy
.请注意,在 Ruby 2.0+ 中,您不需要执行此操作,您可以只使用
Enumerable#lazy
,它返回一个Enumerator::Lazy
。
For reasons that aren't clear to me, Lazy
doesn't have flatten
, but it has flat_map
, so in principle you could just use flat_map
with the identity function .由于我不清楚的原因,
Lazy
没有flatten
,但它有flat_map
,所以原则上你可以使用身份为flat_map
的flat_map 。
module Enumerable
def lazy_flatten
self.lazy.flat_map { |x| x }
end
end
Lazy#flat_map
mostly takes care of decomposing any decomposable elements, but not quite -- from the docs : Lazy#flat_map
主要负责分解任何可分解的元素,但不完全是——来自文档:
A value x returned by block is decomposed if either of the following conditions is true:
如果以下任一条件为真,则块返回的值x将被分解:
- x responds to both
each
andforce
, which means thatx
is a lazy enumerator.x响应
each
和force
,这意味着x
是惰性枚举器。- x is an array or responds to
to_ary
.x是一个数组或响应
to_ary
。
Note that to_ary
is not a method on Enumerable
, presumably to discourage implicit conversions from infinite sequences to arrays. This means, for instance, that if you try to lazy_flatten
something that contains a Set
or a Range
with the above code, it (arguaby, see below) won't work:请注意,
to_ary
不是Enumerable
上的方法,大概是为了阻止从无限序列到 arrays 的隐式转换。这意味着,例如,如果您尝试使用上述代码对包含Set
或Range
的内容进行lazy_flatten
,它(arguaby,见下文)将不起作用:
a = [[1, 2, 3], Set[4, 5], 6, 7..8]
# => [[1, 2, 3], #<Set: {4, 5}>, 6, 7..8]
f = a.lazy_flatten
# => #<Enumerator::Lazy: #<Enumerator::Lazy: [[1, 2, 3], #<Set: {4, 5}>, 6, 7..8]>:flat_map>
f.to_a
# => [1, 2, 3, #<Set: {4, 5}>, 6, 7..8]
However, this is the same as the behavior of Array#flatten
:但是,这与
Array#flatten
的行为相同:
a.flatten
# => [1, 2, 3, #<Set: {4, 5}>, 6, 7..8]
(Although Array#flatten
will not detect and decompose lazy enumerators, and Lazy#flat_map
will.) (尽管
Array#flatten
不会检测和分解惰性枚举器,而Lazy#flat_map
会。)
Whereas the OP's code or the code in Mladen Jablanović's answer will decompose the Set
and the Range
:而 OP 的代码或Mladen Jablanović 的答案中的代码将分解
Set
和Range
:
f = a.lazy_flatten # (M.J.'s code)
# => #<Enumerator: #<Enumerator::Generator:0x00007fd819c166c0>:each>
f.to_a
# => [1, 2, 3, 4, 5, 6, 7, 8]
That code, however, will also iterate infinitely if passed something that includes an infinite sequence:但是,如果传递包含无限序列的内容,该代码也将无限迭代:
a = [[1, 2, 3], Set[4, 5], 6, 7..8, 9..Float::INFINITY]
# => [[1, 2, 3], #<Set: {4, 5}>, 6, 7..8, 9..Infinity]
f = a.lazy_flatten # (M.J.'s code)
# => #<Enumerator: #<Enumerator::Generator:0x00007fd819a73d18>:each>
f.to_a
# => spins at 100% CPU for a while and eventually runs out of memory
If you consider that a feature, rather than a bug, one approach would be to modify the flat_map
-based implementation to convert any enumerables it finds to lazy ones:如果您认为这是一个功能,而不是一个错误,一种方法是修改基于
flat_map
的实现,将它找到的任何可枚举转换为惰性可枚举:
module Enumerable
def lazy_flatten
self.lazy.flat_map do |x|
x.respond_to?(:lazy) ? x.lazy : x
end
end
end
This works even for nested lazy enumerables, as Lazy#lazy
is smart enough to return itself.这甚至适用于嵌套的惰性枚举,因为
Lazy#lazy
足够聪明,可以返回自身。
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