From: "mame (Yusuke Endoh)" Date: 2012-11-24T14:19:48+09:00 Subject: [ruby-core:50018] [ruby-trunk - Feature #6552][Rejected] Enumerator::Generator:select should return another Enumerator::Generator Issue #6552 has been updated by mame (Yusuke Endoh). Status changed from Feedback to Rejected I agree with gregolsen. No feedback. Closing. -- Yusuke Endoh ---------------------------------------- Feature #6552: Enumerator::Generator:select should return another Enumerator::Generator https://bugs.ruby-lang.org/issues/6552#change-33792 Author: eike.rb (Eike Dierks) Status: Rejected Priority: Normal Assignee: Category: core Target version: 1.9.3 The current implementation of Enumerator:select fails when applied to an open ended Enumerator:Generator, resulting in an endless loop. In the current implementation, :select seems to collect all values from the enumerator before applying the selection. If that Enumeration is not bound, this results in an endless loop. Instead, applying :select to a Generator should be applied to each object in turn and should itself return a Enumerator::Generator. For example to select the first 5 even numbers starting at 123 should work as: (123..Float::INFINITY).select{|n|n.even?}.take(5) but this currently results in an endless loop. The same problem applies for :map and some other operators on Enumerations However changing :select and :map to make them work with open ended Enumerations might also change the api contract as they are currently defined to return an array. We might want to have a look at the SICSP on streams, http://mitpress.mit.edu/sicp/full-text/sicp/book/node69.html I came up with this prototype: class Enumerator # return a generator for all elements from enumeration where block returns true def select &block Enumerator.new do |y| self.each do |obj| if block.call(obj) y< [124, 126, 128, 130, 132] voil��! -- http://bugs.ruby-lang.org/