1 // Copyright Louis Dionne 2013-2017
2 // Distributed under the Boost Software License, Version 1.0.
3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
4
5 #include <boost/mpl/equal_to.hpp>
6 #include <boost/mpl/int.hpp>
7 #include <boost/mpl/integral_c.hpp>
8 #include <boost/mpl/minus.hpp>
9 #include <boost/mpl/multiplies.hpp>
10 #include <boost/mpl/pair.hpp>
11 #include <boost/mpl/plus.hpp>
12
13 #include <boost/hana/assert.hpp>
14 #include <boost/hana/concept/constant.hpp>
15 #include <boost/hana/equal.hpp>
16 #include <boost/hana/integral_constant.hpp>
17 #include <boost/hana/minus.hpp>
18 #include <boost/hana/mult.hpp>
19 #include <boost/hana/pair.hpp>
20 #include <boost/hana/plus.hpp>
21
22 #include <type_traits>
23 namespace hana = boost::hana;
24
25
26 namespace support {
27 template <typename T, typename = std::enable_if_t<
28 !hana::Constant<T>::value
29 >>
sqrt(T x)30 constexpr T sqrt(T x) {
31 T inf = 0, sup = (x == 1 ? 1 : x/2);
32 while (!((sup - inf) <= 1 || ((sup*sup <= x) && ((sup+1)*(sup+1) > x)))) {
33 T mid = (inf + sup) / 2;
34 bool take_inf = mid*mid > x ? 1 : 0;
35 inf = take_inf ? inf : mid;
36 sup = take_inf ? mid : sup;
37 }
38
39 return sup*sup <= x ? sup : inf;
40 }
41
42 template <typename T, typename = std::enable_if_t<
43 hana::Constant<T>::value
44 >>
sqrt(T const &)45 constexpr auto sqrt(T const&) {
46 return hana::integral_c<typename T::value_type, sqrt(T::value)>;
47 }
48 } // end namespace support
49
50
51 namespace then {
52 namespace mpl = boost::mpl;
53
54 template <typename N>
55 struct sqrt
56 : mpl::integral_c<typename N::value_type, support::sqrt(N::value)>
57 { };
58
59 template <typename X, typename Y>
60 struct point {
61 using x = X;
62 using y = Y;
63 };
64
65 //! [distance-mpl]
66 template <typename P1, typename P2>
67 struct distance {
68 using xs = typename mpl::minus<typename P1::x,
69 typename P2::x>::type;
70 using ys = typename mpl::minus<typename P1::y,
71 typename P2::y>::type;
72 using type = typename sqrt<
73 typename mpl::plus<
74 typename mpl::multiplies<xs, xs>::type,
75 typename mpl::multiplies<ys, ys>::type
76 >::type
77 >::type;
78 };
79
80 static_assert(mpl::equal_to<
81 distance<point<mpl::int_<3>, mpl::int_<5>>,
82 point<mpl::int_<7>, mpl::int_<2>>>::type,
83 mpl::int_<5>
84 >::value, "");
85 //! [distance-mpl]
86 }
87
88
89 namespace now {
90 namespace hana = boost::hana;
91 using namespace hana::literals;
92
93 template <typename X, typename Y>
94 struct _point {
95 X x;
96 Y y;
97 };
98 template <typename X, typename Y>
point(X x,Y y)99 constexpr _point<X, Y> point(X x, Y y) { return {x, y}; }
100
101 using support::sqrt; // avoid conflicts with ::sqrt
102
103 //! [distance-hana]
104 template <typename P1, typename P2>
distance(P1 p1,P2 p2)105 constexpr auto distance(P1 p1, P2 p2) {
106 auto xs = p1.x - p2.x;
107 auto ys = p1.y - p2.y;
108 return sqrt(xs*xs + ys*ys);
109 }
110
111 BOOST_HANA_CONSTANT_CHECK(distance(point(3_c, 5_c), point(7_c, 2_c)) == 5_c);
112 //! [distance-hana]
113
test()114 void test() {
115
116 //! [distance-dynamic]
117 auto p1 = point(3, 5); // dynamic values now
118 auto p2 = point(7, 2); //
119 BOOST_HANA_RUNTIME_CHECK(distance(p1, p2) == 5); // same function works!
120 //! [distance-dynamic]
121
122 }
123 }
124
125
main()126 int main() {
127 now::test();
128 }
129