Issue #5351 has been updated by Alan Walkings.


Found the same issue with Ruby Enterprise Edition 2011.04
http://informatique.edublogs.org/
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Bug #5351: String#start_with? resets pattern matching results
http://redmine.ruby-lang.org/issues/5351

Author: Ivan Kuznetsov
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 1.8.7 (2011-02-18 patchlevel 334) [x86_64-linux], MBARI 0x6770, Ruby Enterprise Edition 2011.03


String#start_with? backported into 1.8.7 (https://github.com/ruby/ruby/commit/7d848354f8e25a652ccaabbd54e106b44e7da308) has an undocumented behaviour - it resets pattern matching results

Example code:

"Hello".sub!(%r(^(.))) {}
puts "$1 after sub! = '#{$1}'"
"Hello".start_with?("H")  
puts "$1 after start_with? = '#{$1}'"

Ruby 1.8.7:

$1 after sub! = 'H'
$1 after start_with? = '' 

Ruby 1.9.X:

$1 after sub! = 'H'
$1 after start_with? = 'H' 

In Ruby 1.8.7 rb_str_start_with for some reason calls rb_reg_search. In 1.9.X solution is more elegant - memcmp is used: https://github.com/ruby/ruby/blob/ruby_1_9_3/string.c#L7170




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