[ruby-core:45359] [ruby-trunk - Bug #6525][Open] misleading example in Permformance section of Regexp documentation?

Issue #6525 has been reported by nathanst (Nathan Stratton Treadway).

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Bug #6525: misleading example in Permformance section of Regexp documentation?
https://bugs.ruby-lang.org/issues/6525

Author: nathanst (Nathan Stratton Treadway)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: 1.9.3


In the Performance section of the Regexp documention, it is stated  that changing from Regexp.new('a?' * 29 + 'a' * 29) to Regexp.new('\A' 'a?' * 29 + 'a' * 29) speeds up the match significantly.  However, '\A' 'a?' * 29 actually expands to "\\Aa?\\Aa?....\\Aa?" -- which doesn't seem like it's what you'd actually want, since [for example] Regexp.new('\A' 'a?' * 29 + 'a' * 29).match('a' * 50) will only match 30 'a' characters [the 29 from 'a' * 29, plus one single one from the set of '\Aa?' items.  [That is, Regexp.new('\A' 'a?' * 29 + ...) is doesn't match any more 'a' characters than Regexp.new('\A' 'a?' + ...) would.]

One can get around this by changing the expression to Regexp.new('\A' + 'a?' * 29 + 'a' * 29), in which case additional "a" characters do get matched as the string gets longer... but with that Regexp the .match('a' * 29) still takes about the same amount of time as the original one.

So I wonder if there is some better example that could be used here?

Nathan


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