Re: [Boost-users] boost.xpressive: using placeholders with custom (check()) assertions

Subject: Re: [Boost-users] boost.xpressive: using placeholders with custom (check()) assertions
From: Alex Dubov (oakad_at_[hidden])
Date: 2010-06-25 08:32:20

Eric Niebler <eric <at> boostpro.com> writes:

> 
> On 6/16/2010 3:04 AM, Alex Dubov wrote:
> > Greetings.
> > 
> > 
> > However, if functor is wrapped with assertion, this won't work:
> > 
> > sregex r = (expr)[check(do_something(p_string, _))];
> > 
> > Compilation will fail, because do_something has no method which
> > accepts xpressive::placeholder<> objects. 
> 
> It should if it is a lazy function. How is do_something defined? Can you
> send a self-contained program that demonstrates the problem you're having?
> 

I'm using boost-1.41 and gcc-4.4.2. The error I'm receiving compiling an
example:
--------------------------------------------------------------------
testreg1.cpp:51:   instantiated from here
/usr/include/boost/proto/context/default.hpp:426: error: no match for call to
‘(const check_a_impl) (const boost::xpressive::detail::action_arg<int,
mpl_::int_<0> >&, const int&)’
testreg1.cpp:24: note: candidates are: bool check_a_impl::operator()(int&, int)
const

Here goes a problematic example itself:
--------------------------------------------------------------------
#include <iostream>
#include <boost/xpressive/regex_actions.hpp>
#include <boost/xpressive/xpressive_static.hpp>

using namespace std;
using namespace boost::xpressive;

const placeholder<int> _cnt = {{}};

struct count_a_impl {
        typedef void result_type;

        void operator()(int &cnt) const
        {
                ++cnt;
        }
};

function<count_a_impl>::type const count_a = {{}};

struct check_a_impl {
        typedef bool result_type;

        bool operator()(int &cnt, int val) const
        {
                ++cnt;
                return (cnt == val);
        }
};

function<check_a_impl>::type const check_a = {{}};

int main(int argc, char **argv)
{
        int cnt = 0;
        string a_str("a_aaaaa___a_aa_aaa_");
        const sregex expr1(*(as_xpr('a')[count_a(_cnt)] | _));
        const sregex expr2(*(as_xpr('a')[check(check_a(_cnt, 5))] | _));
        /*                               ^ this check() causes a problem */

        sregex_iterator iter1(a_str.begin(), a_str.end(), expr1,
                              let(_cnt = cnt));
        cout << "expr1 matched: " << iter1->str(0) << " counted " << cnt
             << endl;

        cnt = 0;
        sregex_iterator iter2(a_str.begin(), a_str.end(), expr2,
                              let(_cnt = cnt));

        cout << "expr2 matched: " << iter2->str(0) << " counted " << cnt
             << endl;

        return 0;
}