vicente.botet wrote:
Could you tell me if the following is equivalent to what appears in the quick start. I'm not very confortable with foreach.
</code> template<class Range, class Predicate> struct mono_make_filtered { typedef boost::filter_iterator< typename boost::remove_cv<Predicate>::type, typename boost::range_result_iterator<Range>::type > iter_t;
typedef boost::iterator_range<iter_t> result_type;
result_type operator()(Range &rng, Predicate &pred) const { return result_type( iter_t(pred, boost::begin(rng), boost::end(rng)), iter_t(pred, boost::end(rng), boost::end(rng)) ); } };
bool is_not_X(char ch) { return ch != 'X'; } bool is_not_Y(char ch) { return ch != 'Y'; } bool is_lower(char ch) { return std::islower(ch, std::locale()); }
void quick_start_make_filtered() { std::string src("abXcYdXefXgYhY");
mono_make_filtered::result_type lowers = make_filtered(src, &is_lower);
foreach (char ch, lowers) { std::cout << ch; }
foreach (char ch, make_filtered(make_filtered(src, &is_not_X), &is_not_Y)) { std::cout << ch; } } </code>
If this is the case could you show which is really the advantage to use Egg. I 'm sure there are a lot of, but I think the example do not show them.
No, it's not equivalent. mono_make_filtered<std::string, bool(*)(char)>::result_type lowers = ... is equivalent, though. A problem of this form is that users of `make_filtered` have to remember the usage of `mono_make_filtered` instead of the standardized metafunction `result_of`. Regards, -- Shunsuke Sogame