From: Robert Klemme <shortcutter@...>
Date: 2007-05-02T22:25:04+09:00
Subject: Re: Inverse scanf: finding format specifers of existing fields

On 02.05.2007 15:08, Bil Kleb wrote:
> Robert Klemme wrote:
>>
>> If there is a fixed number of formats you can probably use a cascade 
>> of RX matches.
> 
> Unfortunately not.
> 
>> Otherwise it probably becomes a bit more complex like matching 
>> sequences of digits and measuring their lengths.
>>
>>  >> md = %r{^(\d+)\.(\d+)?$}.match('0.4577')
>> => #<MatchData:0x7ef61250>
>>  >> pa="%#{md[0].size}.#{md[2].size}f"
> 
> Hmmm, this looks like a viable path.
> 
> I hadn't thought of using MatchData groups, but as you say,
> it may get ugly fast...  I'm thinking of edge cases like
> dealing with the leading space if positive numbers become
> negative, or accommodating the number of digits needed for
> exponentials or integers if the new number exceeds the
> capacity of the existing format.

For floating point numbers you might even get away with a single regexp 
if that is crafted appropriately and group values are evaluated accordingly.

Kind regards

	robert