Bug #7248
closedShouldn't Enumerator::Lazy.new be private?
Added by marcandre (Marc-Andre Lafortune) almost 12 years ago. Updated over 11 years ago.
Description
Is there a reason why Enumerator::Lazy.new is not private?
Lazy enumerators should be created with Enumerable#lazy
. Moreover, there is no doc, and it can give unexpected results too.
Updated by mame (Yusuke Endoh) almost 12 years ago
- Status changed from Open to Assigned
- Assignee set to yhara (Yutaka HARA)
Yhara-san, I'd like your opinion about this ticket.
--
Yusuke Endoh mame@tsg.ne.jp
Updated by yhara (Yutaka HARA) over 11 years ago
Hi,
Enumerator::Lazy.new will be needed
(1) when you want to overwrite behavior of a lazy method. eg:
class Enumerator::Lazy
def zip(*args, &block)
enums = args.map(&:lazy)
Lazy.new(self){|yielder, val|
ary = [val] + enums.map{|e| e.next}
if block
yielder << block.call(ary) # make lazy.zip{} behave lazy (currently it doesn't because enum.zip{} is eager)
else
yielder << ary
end
}
end
end
fizz = [nil, nil, nil, nil, "Fizz"].cycle
buzz = [nil, nil, "Buzz"].cycle
p fizz.lazy.zip(buzz){|f, b| "#{f}#{b}"}.first(20)
(2) when you want to add a new Enumerable method and its lazy version. eg:
module Enumerable
def filter_map(&block)
self.map(&block).compact
end
end
class Enumerator::Lazy
def filter_map(*args, &block)
Lazy.new(self){|yielder, val|
result = block.call(val)
yielder << result if result
}
end
end
p [11,12,13].filter_map{|i| ii if i.even?} #=> [144]
p (1..Float::INFINITY).lazy.filter_map{|i| ii if i.even?}.first(20)
Updated by marcandre (Marc-Andre Lafortune) over 11 years ago
Oh, interesting.
I'll do my best to document it, then.
This leads to more questions, though:
- Is there a use case for the form without a block?
It's used internally (before calling lazy_set_method), but other than that I can't see a good use.
- Is there a use case for specifying a symbol and arguments?
Again, internally we call lazy_set_method, to the symbol and arguments are only used by inspect, right?
-
Is there a good way to improve the
inspect
of such a lazy enum?p [11,12,13].filter_map{|i| i*i if i.even?} # => #<Enumerator::Lazy: #<Enumerator::Lazy: [1, 2, 3]>:each>
Notice the each
and no appearance of filter_map
Doing Lazy.new(self, :filter_map)
does not work and seems redundant.
Thanks
BTW, ultimately, I'm trying to see if Lazy.new can be adapted to accept a size
lambda argument...
Updated by yhara (Yutaka HARA) over 11 years ago
- Assignee changed from yhara (Yutaka HARA) to marcandre (Marc-Andre Lafortune)
marcandre (Marc-Andre Lafortune) wrote:
Oh, interesting.
I'll do my best to document it, then.
Thanks!
This leads to more questions, though:
- Is there a use case for the form without a block?
It's used internally (before calling lazy_set_method), but other than that I can't see a good use.
That form is only for internal use.
You can remove the form without a block by replacing Lazy.new(enum)' with
Lazy.new(enum){|y, v| y<<v}'.
- Is there a use case for specifying a symbol and arguments?
Actually I did not know lazy_initialize can take a symbol :-p
So I'm not sure about how the symbol and arguments are used,
but it looks like for internal use.
According to svn annotate, it is introduced to implement lazy.cycle (r35028).
Again, internally we call lazy_set_method, to the symbol and arguments are only used by inspect, right?
That seems right.
Is there a good way to improve the
inspect
of such a lazy enum?p [11,12,13].filter_map{|i| i*i if i.even?} # => #<Enumerator::Lazy: #<Enumerator::Lazy: [1, 2, 3]>:each>
Notice the
each
and no appearance offilter_map
Doing
Lazy.new(self, :filter_map)
does not work and seems redundant.BTW, ultimately, I'm trying to see if Lazy.new can be adapted to accept a
size
lambda argument...
Well, I have no idea. It would be difficult to design Lazy.new which may take
obj, block, symbol, args and size/size_fn...
BTW, I have a question. Document of to_enum says "see Enumerator#size=" but there is no such method. Is it a typo?
https://github.com/ruby/ruby/blob/e90ccd3beb0b9bf1125461ef68943578739bebbe/enumerator.c#L201
Updated by marcandre (Marc-Andre Lafortune) over 11 years ago
- Priority changed from Normal to 5
Thanks for the answers.
So, the public API of Lazy.new has the following issues:
- not documented
- should require a block but doesn't
- accepts a method name & arguments which aren't really usable
- has a misleading "inspect"
Moreover, the only way for the user to create a lazy enumerator with a size is to subclass Lazy.
Here's what I propose as the official Lazy.new documentation and API:
Lazy.new(obj, size=nil) { |yielder, *values| ... }
Creates a new Lazy enumerator. When the enumerator is actually enumerated
(e.g. by calling #force), +obj+ will be enumerated and each value passed
to the given block. The block can yield values back using +yielder+.
For example, to create a method +filter_map+ in both lazy and
non-lazy fashions:
module Enumerable
def filter_map(&block)
map(&block).compact
end
end
class Enumerator::Lazy
def filter_map
Lazy.new(self) do |yielder, *values|
result = yield *values
yielder << result if result
end
end
end
(1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.first(5)
# => [4, 16, 36, 64, 100]
Does this seem acceptable to you?
We should also change the result of the 'inspect' method for these user created lazy enumerators to remove the 'each', i.e:
(1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.inspect
# => #<Enumerator::Lazy: #<Enumerator::Lazy: 1..Infinity>>
If we want to provide an easy way to provide more info in the inspect, we could add extra parameters, but they shouldn't be used when iterating, only for inspection...
BTW, I have a question. Document of to_enum says "see Enumerator#size=" but there is no such method. Is it a typo?
Typo fixed, thanks.
Updated by marcandre (Marc-Andre Lafortune) over 11 years ago
- Assignee changed from marcandre (Marc-Andre Lafortune) to yhara (Yutaka HARA)
Updated by yhara (Yutaka HARA) over 11 years ago
- Assignee changed from yhara (Yutaka HARA) to marcandre (Marc-Andre Lafortune)
marcandre (Marc-Andre Lafortune) wrote:
Here's what I propose as the official Lazy.new documentation and API:
Lazy.new(obj, size=nil) { |yielder, *values| ... } Creates a new Lazy enumerator. When the enumerator is actually enumerated (e.g. by calling #force), +obj+ will be enumerated and each value passed to the given block. The block can yield values back using +yielder+. For example, to create a method +filter_map+ in both lazy and non-lazy fashions: module Enumerable def filter_map(&block) map(&block).compact end end class Enumerator::Lazy def filter_map Lazy.new(self) do |yielder, *values| result = yield *values yielder << result if result end end end (1..Float::INFINITY).lazy.filter_map{|i| i*i if i.even?}.first(5) # => [4, 16, 36, 64, 100]
Does this seem acceptable to you?
Yes!
Updated by marcandre (Marc-Andre Lafortune) over 11 years ago
- Status changed from Assigned to Closed
- % Done changed from 0 to 100
This issue was solved with changeset r39057.
Marc-Andre, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
-
enumerator.c: Finalize and document Lazy.new. [Bug #7248]
Add Lazy#to_enum and simplify Lazy#size. -
test/ruby/test_lazy_enumerator.rb: tests for above