From: Rob Biedenharn <Rob@...>
Date: 2010-08-20T00:42:53+09:00
Subject: Re: ambiguous first argument?

On Aug 19, 2010, at 11:26 AM, Gianfranco Bozzetti wrote:

> Roger Pack wrote:
>> Hi all.
>> With this code:
>>
>> memory_bitmap.scan /\x00{5}+/
>>
>> I get this warning:
>>
>> test.rb:1: warning: ambiguous first argument; put parentheses or even
>> spaces
>>
>> Could somebody please help me to understand what exactly is ambiguous
>> there?
>> Thank you!
>> -r
>
> The ambiguity comes from the double quantifier {5}+ where:
> - {5} means exactly 5 occurrences of \x00
> - +   means 1 or more occurrences of preceding expression.
>
> Given the string:
> bitmap="\x30\x50\-\x00\x00\x00\x00\x00\x00\-\x40\x50\x30"
>
> p bitmap.scan(/\x00+/)       #=> ["\000\000\000\000\000\000"]
> p bitmap.scan(/\x00{2}/)     #=> ["\000\000", "\000\000", "\000\000"]
>
> HTH gfb
> --  
> Posted via http://www.ruby-forum.com/.
>


I think the ambiguity is actually in parsing:

memory_bitmap.scan / \x00 { 5 } + /
Is that perhaps dividing by the result of calling \x00 with a block?

Spaces won't help in this case, but some nice parentheses will do.

memory_bitmap.scan(/\x00{5}+/)

That will ensure that the parser sees /\x00{5}+/ as an argument to the  
scan method.  Whether the Regexp does what you want/expect is another  
question.

-Rob

Rob Biedenharn		
Rob@AgileConsultingLLC.com	http://AgileConsultingLLC.com/
rab@GaslightSoftware.com		http://GaslightSoftware.com/