On 19/12/2010 19:40, Brent Spillner wrote:
I uploaded sample code to the Vault (in the "Miscellaneous/" directory) that provides a concise notation for list comprehensions. The comprehensions are evaluated lazily and can be used to populate a std::list, vector, or deque, appended to the same, inserted after a given iterator, or interpreted as a boost::range, including compatibility with BOOST_FOREACH. Containers, iterator-defined ranges, or nullary function objects can be used as generators, and arbitrary function objects can be used to specify filter conditions.
Can you explain the difference with the Boost.Range adaptors?
For example, the Pythagorean Triples example from http://rosettacode.org/wiki/List_comprehensions can be coded as
std::vector< boost::tuple<int,int,int> > triples =_(x, y, z)[x<<= range(1, n), y<<= range(x, n), z<<= range(y, n), x*x + y*y == z*z];
Here is the approximation of this with Boost.Range : auto r = combine(irange(1, n), irange(1, n), irange(1, n)) | filtered(at_c<0>(_1)*at_c<0>(_1) + at_c<1>*at_c<1> == at_c<2>*at_c<2>); std::vector< boost::tuple<int, int, int> > triples(r.begin(), r.end()); It doesn't support tuples with an easy syntax like you do, and there is no way to define dependencies between the tuple elements. It is true Boost.Range is quite lacking in terms of range generators, and maybe your solution is what we need. It would be nice however, if it didn't reinvent the wheel and can be based on Phoenix for the functional part.