Feature #707: Documentation for Enumerator chaining

• Status: Closed
• Assignee: drbrain (Eric Hodel)
• Target version: 2.0.0

[candlerb (Brian Candler)]

=begin
Enumerators now support a horizontal filter/chaining pattern:

generator.filter1 { ... }.filter2 { ... }.filter3 { ... }.consumer

The overall pattern for a filter is:

Enumerator.new do |y|
source.each do |input| # filter INPUT
...
y << output # filter OUTPUT
end
end

This is extremely powerful. However it is not obvious to the newcomer that this is even possible. (Confusion may arise where people know Ruby 1.8's Enumerator, which cannot do this)

So I would just like to see this pattern documented with an example, e.g. under ri Enumerator.new

I have attached a possible example. Note that I have written my Fib generator in a style familiar from ruby-1.8, to emphasise that the Enumerator filter doesn't require a specially-written generator.
=end

[candlerb (Brian Candler)]

=begin
Here is another (shorter and simpler)

class Enumerator
def filter(&blk)
self.class.new do |y|
each do |*input|
blk.call(y, *input)
end
end
end
end

a = (1..1_000_000_000).to_enum
a.filter { |out,inp| out << inp if inp % 2 == 0 }.
filter { |out,inp| out << inp+100 }.
with_index.each { |inp,c| puts inp; break if c > 10 }

=end

[ko1 (Koichi Sasada)]

• Assignee set to matz (Yukihiro Matsumoto)

=begin

=end

[rogerdpack (Roger Pack)]

=begin
Is this also possible in 1.8?

http://www.ruby-forum.com/topic/198804#new
http://github.com/trans/facets/blob/master/lib/core/facets/denumerable.rb

Brian do you think you could write the tutorial on chaining started here:
http://wiki.github.com/rdp/ruby_tutorials_core/enumerator
?
-r
=end

[candlerb (Brian Candler)]

=begin

Is this also possible in 1.8?

Sure. Block-form Enumerator is surprisingly straightforward to implement, see
http://github.com/trans/facets/blob/master/lib/more/facets/enumerator.rb

But since 1.9 has it already, I think it's worth documenting the possibilities more clearly.
=end

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

=begin

=end

[mame (Yusuke Endoh)]

• Assignee changed from matz (Yukihiro Matsumoto) to drbrain (Eric Hodel)

Drbrain, could you take over this documentation ticket?

--
Yusuke Endoh [e-mail]

[drbrain (Eric Hodel)]

• Priority changed from 3 to Normal

I will work on it, thank you.

[drbrain (Eric Hodel)]

• File enumerator.c.lazy.patch enumerator.c.lazy.patch added

What do you think about this patch?

I chose not to monkey-patch Enumerator since I don't want the documentation to collide with #4890

Also, I think assigning the lazy enumerators helps illustrate the difference between lazy_select and select (select would never return).

[mame (Yusuke Endoh)]

Look good to me. Please go ahead!

--
Yusuke Endoh [e-mail]

[drbrain (Eric Hodel)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r34586.
Brian, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• enumerator.c: Document use of Enumerator.new for creating a lazy
  enumeration for filtering/chaining. [ruby-trunk - Feature #707]