2015-06-22 16:17 GMT+02:00 Tobias Loew <Tobias.Loew@steag.com>:
Sorry for that,
I've made in implementation with free functions which compiles on VS 2012:
#include <assert.h> #include <boost/optional.hpp>
template<class T, class B> auto bind(const boost::optional<T>& optional, B&& binder) -> typename std::decay<decltype(std::bind(binder, *optional)())>::type { if(optional) { return std::bind(binder, *optional)(); } else { return boost::none; } }
template<class T, class B> auto map(const boost::optional<T>& optional, B&& binder) -> boost::optional<typename std::decay<decltype(std::bind(binder, *optional)())>::type> { if(optional) { return std::bind(binder, *optional)(); } else { return boost::none; } }
void foo() { struct A { int i; }; boost::optional<A> opt_a;
auto opt_i = map(opt_a, &A::i); assert(!opt_i);
A a = {42}; opt_a = a;
auto opt_i2 = map(opt_a, &A::i); assert(*opt_i2 == 42);
}
Would you find the following an acceptable solution? ``` #include <assert.h> #include <boost/bind.hpp> #include <boost/optional.hpp> template <typename T, typename F> auto map2(const boost::optional<T>& o, F f) -> boost::optional<decltype(f(*o))> { if (o) return f(*o); else return boost::none; } void foo() { struct A { int i; }; boost::optional<A> opt_a; auto opt_i = map2(opt_a, boost::bind(&A::i, _1)); assert(!opt_i); A a = {42}; opt_a = a; auto opt_i2 = map2(opt_a, boost::bind(&A::i, _1)); assert(opt_i2); assert(*opt_i2 == 42); } int main() { foo(); } ``` It requires of you to type a bit more, but at the same time it is more flexible: you can type any free function on T, including a lambda. Regards, &rzej