Issue #3388 has been updated by akr.


I think we can cache regexp structure according to regexp source, options, encoding.

If regexp structure is cached, /\A#{pattern}/ and /#{pattern}\z/ is not slow for
 second and successive dynamic regexp creation.

If it is not slow, we can use them to implement String#{start_with?,end_with?} for regexp.

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Feature #3388: regexp support for start_with? and end_with?
https://bugs.ruby-lang.org/issues/3388#change-24718

Author: trans
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


=begin
 ruby-1.9.2-head > "aBcdeFghIj".start_with?(/abc/i)
 => false 
 
 In my implementation of start_with? it is easy enough to utilize #index, which works fine:
 
   def start_with?(pattern)
     index(pattern) == 0
   end
 
 But #end_with? is more difficult, and I had to use regular expressions.
 
     def end_with?(suffix)
       suffix = Regexp.escape(suffix) if String===suffix
       /#{suffix}$/.match(self) ? true : false
     end
 
 However, we might get rid of the '? true : false' and return the MatchData, since that could be useful information.
=end



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