2013/6/6 Akira Takahashi <faithandbrave@gmail.com>
Hi Michel, ... I see. `optional_front` usage is following:
if (optional<T> x = r | optional_front()) { std::cout << x.get() << std::endl; }
If `front` return signle range, the usage is following:
for (T x : x | front) { std::cout << x << std::endl; }
If `front` is error, the return value is empty range. I think single range approach is better. However, I think now `front` and `optional_front` is useful.
I would like to add `optional_front` and `front_range`.
I implemented `optional_front`, `optional_back`, and `optional_at`. https://github.com/faithandbrave/OvenToBoost/commit/3c828848be96de1c7d5d17a9... usage: #include <iostream> #include <vector> #include <boost/assign/list_of.hpp> #include <boost/range/adaptor/filtered.hpp> #include <boost/range/access/front.hpp> bool is_even(int x) { return x % 2 == 0; } int main() { using namespace boost::adaptors; using namespace boost::range::access; std::vector<int> v = boost::assign::list_of(1)(2)(3); if (boost::optional<int&> x = v | filtered(is_even) | optional_front) { std::cout << x.get() << std::endl; } else { std::cout << "not found" << std::endl; } } result: 2 Thanks, Akira
======================== Akira Takahashi mailto:faithandbrave@gmail.com site : https://sites.google.com/site/faithandbrave/about/en