Re: [Boost-users] [regex] Context-sensitive replacement of textusingregex_replace

Subject: Re: [Boost-users] [regex] Context-sensitive replacement of textusingregex_replace
From: Eric Niebler (eric_at_[hidden])
Date: 2009-02-25 13:46:13

John Maddock wrote:
>> Having done something similar a number of times, I wonder if it
>> would be worth implementing a variant of regex_replace where a
>> functor is called that accepts the matched string and returns the
>> replacement string.
>> 
>> I think this is a common usage scenario.
> 
> Me too: I was thinking exactly this as I wrote that reply,  I'll try
> and add this for the next release - can I get you to file a feature
> request at svn.boost.org so I don't forget?

I don't think such a callback would be useful to the OP. If the callback 
merely accepts the matched string, it would need to reparse the string 
to find the sub-matches. In addition, accepting and returning strings 
imposes unnecessary dynamic allocations.

Xpressive's regex_replace() algorithm can accept a formatter function or 
function object with one of three different signatures. It can either:

a) Accept the match_results object, and return a std::string, or
b) Accept the match_results object and an output iterator, and return
    the output iterator, or
b) Accept the match_results object, an output iterator and the match
    flags, and return the output iterator.

You can read about it here: http://tinyurl.com/bd6c3f. I like this 
interface because it gives the formatter object lots of context and 
makes formatting potentially very efficient.

It would be great if Boost.Regex and Boost.Xpressive settled on a common 
callback interface for regex_replace().

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com