Eric Niebler skrev:
Thorsten Ottosen wrote:
Then, other return ranges could be specified in this EDSL as
boost::find[_f+_1,e_]( rng | filtered ); boost::find[_f-_1,e_]( rng | filtered ); boost::find[_b,_f+_1]( rng | filtered ); boost::find[_b,_f]( rng | filtered ); boost::find[_b,_f+_1]( rng | filtered );
Interesting! That's really not half bad.
and perhaps even allow
boost::find[_b+_next(n),_f]( rng | filtered );
Whoa. That could make it too easy to create invalid ranges, but way to think outside the box!
Yeah, implementing e.g. boost::find[_f+_1,_e]( rng | filtered ); is easier because we only the expression _f+_1,_e to generate a type. With _b+_next(n),_f it would be a type and an embedded number. Notice, however, that one major motivation to let this knowledge be known to the algorithm is, perhaps surprising, that it makes it almost impossible to form invalid ranges --- something that is quite easy otherwise. The cannonical example is already in Neil's docs: """ For example, consider how easy we may erase the duplicates in a sorted container: std::vector<int> vec = ...; boost::erase( vec, boost::unique<boost::return_found_end>( boost::sort(vec) ) ); Notice the use of boost::return_found_end. What if we wanted to erase all the duplicates except one of them? In old-fashioned STL-programming we might write // assume 'vec' is already sorted std::vector<int>::iterator i = std::unique( vec.begin(), vec.end() ); // remember this check or you get into problems if( i != vec.end() ) ++i; vec.erase( i, vec.end() ); The same task may be accomplished simply with boost::erase( vec, boost::unique<boost::return_next_end>(vec) ); """ Now, as for the possibility that _b+_next(n),_f-_prev(m) would generate invalid ranges, then I guess that is true. But the algorithm should easily be able to catch this with an assertion. If you adjusted the range manually, afterwards, you would have the same possibility to generate invalid ranges and not get the assertion that the library provides (of course, the debug-iterators might catch this, if your library supports them). -Thorsten