compile with clang++ --std=c++11 maybe.cpp

gistfile1.cpp

#include <cstdio>
#include <boost/optional.hpp>

template <class T>
using Maybe = boost::optional<T>;

Maybe<int> isYouPositive(int val)
{
    return val > 0 ? Maybe<int>(val) : Maybe<int>();
}

int main(void) 
{
    auto valid = isYouPositive(1);
    auto invalid = isYouPositive(-1);
    printf("%d\n", valid.get());
    printf("%d\n", invalid.get());
}

compile with clang++ --std=c++11 maybe.cpp