#define BOOST_HANA_CONFIG_ENABLE_STRING_UDL


namespace hana = boost::hana;

using namespace hana::literals;

using hana::make_map, hana::insert, hana::make_pair, hana::_, hana::always, hana::traits::is_same, hana::decltype_;


int main() {
 auto foo = insert(insert(make_map(), make_pair("a"_s, [](auto x) { return x; })), make_pair("b"_s, [] { return "co"; }));
 
 
 auto call = [=](auto name, auto ... args) {
   return foo[name](args...);
 };
 
 auto reta = call("a"_s, 1);
 auto retb = call("b"_s, 2);
 
 static_assert(is_same(decltype_(reta), decltype_(2)));
 static_assert(is_same(decltype_(retb), hana::type_c<const char *>));
}

use std::ops::Add;

struct Point2d<T> {
   a: T,
   b: T
}

impl<T: Add<Output=T>> Add for Point2d<T> {
   type Output = Self;
   fn add(self, other: Self) -> Self::Output {
       Self {
           a: self.a + other.a,
           b: self.b + other.b,
       }
   }
}

fn main() {
   let x = Point2d { a: 0, b: 0 } + Point2d { a: 42, b: 42 };
   let y = Point2d { a: (), b: () } + Point2d { a: (), b: () };
   //  --> main.rs:21:38
   //   |
   //21 |     let y = Point2d { a: (), b: () } + Point2d { a: (), b: () };
   //   |             ------------------------ ^ ------------------------ Point2d<()>
   //   |             |
   //   |             Point2d<()>
   //   |
   //   = note: an implementation of `std::ops::Add` might be missing for `Point2d<()>`

}