Re: [boost] Regex ease-of-use ideas

From: Allan Odgaard (ML_at_[hidden])
Date: 2004-04-05 16:55:51

On 5. Apr 2004, at 21:22, David Abrahams wrote:

> 1. There's no way to search a stream for a match because a regex
>    requires bidirectional iterators, so I have to do this totally
>    frustrating line-by-line search.  I think Spirit has some kind of
>    iterator that turns an input iterator into something forward by
>    holding a cache of the data starting with the earliest copy of the
>    original iterator.  Could something like that be added?

Added only to the regex library? sounds like it would be a very useful 
general purpose iterator adaptor, as there are also other (non 
standard) algorithms which need to backtrack over the input.

> 2. Seems to me that if match objects could be converted to bool, we
>    might be able to:

I can only second that, I am currently using my own regex library (some 
of my reasoning to be found in this c.l.c++.m thread: 
<http://tinyurl.com/2xnbd>), here I also allow implicit conversion to 
the iterator type, which allow code like:

    iterator it = regex:find(first, last, ptrn);

Although I already did propose it for boost, but was told that it poses 
a problem with the ambiguity of an "empty" match at the end of the 
string and "no match at all" -- my argument here is that if one knows 
that the pattern might generate such a match (and one is interested in 
knowing about it), one just declares the result to be the match object. 
The former generally allows to code w/o all those if's to see if 
something was actually matched -- at least it has made much of my code 
simpler/shorter.

>         if (boost::smatch m = boost::regex_match(line, pat))

or:      if (boost::smatch const& m = boost::regex_match(line, pat))

>    [...] Are match objects expensive to construct?

At least they do not have to be :)