From: mame@...
Date: 2015-12-13T08:11:39+00:00
Subject: [ruby-core:72094] [Ruby trunk - Bug #11811] Chaining lazy enumerators causes duplicate ouput

Issue #11811 has been updated by Yusuke Endoh.


Not only reject's bug.  Lazy enumerator ignores &:method generally.

~~~~
$ ./miniruby -e '

s = [1,2,3].lazy.map(&:nonexist)
p :foo
s.each {|x| p x; 100 + x }

'
:foo
1
101
2
102
3
103
~~~~

Correct behavior:

~~~
$ ruby -ve '

s = [1,2,3].lazy.map(&:nonexist)
p :foo
s.each {|x| p x; 100 + x }

'
ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-linux]
:foo
-e:5:in `each': undefined method `nonexist' for 1:Fixnum (NoMethodError)
~~~

Explicit `.to_proc` works correctly.

~~~
$ ./miniruby -e '

s = [1,2,3].lazy.map(&:nonexist.to_proc)
p :foo
s.each {|x| p x; 100 + x }

'
:foo
-e:5:in `each': undefined method `nonexist' for 1:Fixnum (NoMethodError)
~~~

So I guess this is caused by nobu's optimization.

-- 
Yusuke Endoh <mame@ruby-lang.org>

----------------------------------------
Bug #11811: Chaining lazy enumerators causes duplicate ouput
https://bugs.ruby-lang.org/issues/11811#change-55510

* Author: Chris Beer
* Status: Open
* Priority: Normal
* Assignee: Nobuyoshi Nakada
* ruby -v: ruby 2.3.0preview2 (2015-12-11 trunk 53028) [x86_64-darwin15]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
In Ruby 2.3.0-preview2, I'm seeing a change in behavior using lazy enumerators with select/reject and the & operator:

irb(main):037:0> %w(1 2 3).lazy.reject(&:empty?).each { |x| puts x }
1
1
2
2
3
3

Note that the output is doubled. However, if I don't use the & shorthand, the output is as expected:


irb(main):038:0> %w(1 2 3).lazy.reject { |x| x.empty? }.each { |x| puts x }
1
2
3
=> nil


And in Ruby 2.2.3, both variants produced the same result:

irb(main):001:0> %w(1 2 3).lazy.reject(&:empty?).each { |x| puts x }
1
2
3
=> nil




-- 
https://bugs.ruby-lang.org/