From: Ryan Davis <ryand-ruby@...>
Date: 2010-04-16T05:31:42+09:00
Subject: [ruby-core:29540] Re: [Bug #3152] StringScanner is failing with symbols like # or {


On Apr 15, 2010, at 07:52 , Petr Kovar wrote:

> Bug #3152: StringScanner is failing with symbols like # or {
> http://redmine.ruby-lang.org/issues/show/3152
> 
> Author: Petr Kovar
> Status: Open, Priority: Normal
> ruby -v: all versions
> 
> StringScanner has problems with symbols like # or { in the middle of a text.
> If a string starts with the symbols, it's ok.
> Function scan_until, however, works well. Problematic functions are
> scan and scan_full.
> 
> Example:
> 
> require 'strscan'
> 
> s1 = StringScanner.new('#{expr} blah blah')
> s2 = StringScanner.new('blah blah #{expr} blah blah')
> reg = /#\{/
> 
> puts "s1 failed" unless s1.scan(reg) # should be ok
> puts "s2 failed" unless s2.scan(reg) # is failing

StringScanner#scan != String#scan

You need to get the scanner up to the "#{" in s2 for it to work:

require 'strscan'

s1 = StringScanner.new('#{expr} blah blah')
s2 = StringScanner.new('blah blah #{expr} blah blah')
reg = /#\{/

puts "s1 failed" unless s1.scan(reg) # should be ok

s2.scan(/(?:blah )+/) # need to 

puts "s2 failed" unless s2.scan(reg) # is failing

See ri for another example:

> % ri StringScanner.scan
> = StringScanner.scan
> 
> Tries to match with pattern at the current position. If there's a match, the
> scanner advances the "scan pointer" and returns the matched string. Otherwise,
> the scanner returns nil.
> 
>   s = StringScanner.new('test string')
>   p s.scan(/\w+/)   # -> "test"
>   p s.scan(/\w+/)   # -> nil
>   p s.scan(/\s+/)   # -> " "
>   p s.scan(/\w+/)   # -> "string"
>   p s.scan(/./)     # -> nil