1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 // UNSUPPORTED: c++03, c++11, c++14, c++17
10 // UNSUPPORTED: libcpp-no-concepts
11 
12 // <compare>
13 
14 // template<class T> constexpr weak_ordering weak_order(const T& a, const T& b);
15 
16 #include <compare>
17 
18 #include <cassert>
19 #include <cmath>
20 #include <iterator> // std::size
21 #include <limits>
22 #include <type_traits>
23 #include <utility>
24 
25 #include "test_macros.h"
26 
27 template<class T, class U>
28 constexpr auto has_weak_order(T&& t, U&& u)
29     -> decltype(std::weak_order(static_cast<T&&>(t), static_cast<U&&>(u)), true)
30 {
31     return true;
32 }
33 
34 constexpr bool has_weak_order(...) {
35     return false;
36 }
37 
38 namespace N11 {
39     struct A {};
40     struct B {};
41     std::strong_ordering weak_order(const A&, const A&) { return std::strong_ordering::less; }
42     std::strong_ordering weak_order(const A&, const B&);
43 }
44 
45 void test_1_1()
46 {
47     // If the decayed types of E and F differ, weak_order(E, F) is ill-formed.
48 
49     static_assert( has_weak_order(1, 2));
50     static_assert(!has_weak_order(1, (short)2));
51     static_assert(!has_weak_order(1, 2.0));
52     static_assert(!has_weak_order(1.0f, 2.0));
53 
54     static_assert( has_weak_order((int*)nullptr, (int*)nullptr));
55     static_assert(!has_weak_order((int*)nullptr, (const int*)nullptr));
56     static_assert(!has_weak_order((const int*)nullptr, (int*)nullptr));
57     static_assert( has_weak_order((const int*)nullptr, (const int*)nullptr));
58 
59     N11::A a;
60     N11::B b;
61     static_assert( has_weak_order(a, a));
62     static_assert(!has_weak_order(a, b));
63 }
64 
65 namespace N12 {
66     struct A {};
67     std::strong_ordering weak_order(A&, A&&) { return std::strong_ordering::less; }
68     std::strong_ordering weak_order(A&&, A&&) { return std::strong_ordering::equal; }
69     std::strong_ordering weak_order(const A&, const A&);
70 
71     struct B {
72         friend std::partial_ordering weak_order(B&, B&);
73     };
74 
75     struct WeakOrder {
76         explicit operator std::weak_ordering() const { return std::weak_ordering::less; }
77     };
78     struct C {
79         bool touched = false;
80         friend WeakOrder weak_order(C& lhs, C&) { lhs.touched = true; return WeakOrder(); }
81     };
82 }
83 
84 void test_1_2()
85 {
86     // Otherwise, weak_ordering(weak_order(E, F))
87     // if it is a well-formed expression with overload resolution performed
88     // in a context that does not include a declaration of std::weak_order.
89 
90     // Test that weak_order does not const-qualify the forwarded arguments.
91     N12::A a;
92     assert(std::weak_order(a, std::move(a)) == std::weak_ordering::less);
93     assert(std::weak_order(std::move(a), std::move(a)) == std::weak_ordering::equivalent);
94 
95     // The type of weak_order(e,f) must be explicitly convertible to weak_ordering.
96     N12::B b;
97     static_assert(!has_weak_order(b, b));
98 
99     N12::C c1, c2;
100     ASSERT_SAME_TYPE(decltype(std::weak_order(c1, c2)), std::weak_ordering);
101     assert(std::weak_order(c1, c2) == std::weak_ordering::less);
102     assert(c1.touched);
103     assert(!c2.touched);
104 }
105 
106 template<class F>
107 constexpr bool test_1_3()
108 {
109     // Otherwise, if the decayed type T of E is a floating-point type,
110     // yields a value of type weak_ordering that is consistent with
111     // the ordering observed by T's comparison operators and strong_order,
112     // and if numeric_limits<T>::is_iec559 is true, is additionally consistent with
113     // the following equivalence classes...
114 
115     // std::numeric_limits<F>::is_iec559 is usually true.
116     // It is false for F=long double on AIX; but this test is still expected
117     // to pass (e.g. std::weak_order(+0, -0) == weak_ordering::equivalent,
118     // even on AIX).
119 
120     ASSERT_SAME_TYPE(decltype(std::weak_order(F(0), F(0))), std::weak_ordering);
121 
122     F v[] = {
123         -std::numeric_limits<F>::infinity(),
124         std::numeric_limits<F>::lowest(),  // largest (finite) negative number
125         F(-1.0), F(-0.1),
126         -std::numeric_limits<F>::min(),    // smallest (normal) negative number
127         F(-0.0),                           // negative zero
128         F(0.0),
129         std::numeric_limits<F>::min(),     // smallest (normal) positive number
130         F(0.1), F(1.0), F(2.0), F(3.14),
131         std::numeric_limits<F>::max(),     // largest (finite) positive number
132         std::numeric_limits<F>::infinity(),
133     };
134 
135     static_assert(std::size(v) == 14);
136 
137     // Sanity-check that array 'v' is indeed in the right order.
138     for (int i=0; i < 14; ++i) {
139         for (int j=0; j < 14; ++j) {
140             auto naturalOrder = (v[i] <=> v[j]);
141             if (v[i] == 0 && v[j] == 0) {
142                 assert(naturalOrder == std::partial_ordering::equivalent);
143             } else {
144                 assert(naturalOrder == std::partial_ordering::unordered || naturalOrder == (i <=> j));
145             }
146         }
147     }
148 
149     assert(std::weak_order(v[0], v[0]) == std::weak_ordering::equivalent);
150     assert(std::weak_order(v[0], v[1]) == std::weak_ordering::less);
151     assert(std::weak_order(v[0], v[2]) == std::weak_ordering::less);
152     assert(std::weak_order(v[0], v[3]) == std::weak_ordering::less);
153     assert(std::weak_order(v[0], v[4]) == std::weak_ordering::less);
154     assert(std::weak_order(v[0], v[5]) == std::weak_ordering::less);
155     assert(std::weak_order(v[0], v[6]) == std::weak_ordering::less);
156     assert(std::weak_order(v[0], v[7]) == std::weak_ordering::less);
157     assert(std::weak_order(v[0], v[8]) == std::weak_ordering::less);
158     assert(std::weak_order(v[0], v[9]) == std::weak_ordering::less);
159     assert(std::weak_order(v[0], v[10]) == std::weak_ordering::less);
160     assert(std::weak_order(v[0], v[11]) == std::weak_ordering::less);
161     assert(std::weak_order(v[0], v[12]) == std::weak_ordering::less);
162     assert(std::weak_order(v[0], v[13]) == std::weak_ordering::less);
163     assert(std::weak_order(v[1], v[0]) == std::weak_ordering::greater);
164     assert(std::weak_order(v[1], v[1]) == std::weak_ordering::equivalent);
165     assert(std::weak_order(v[1], v[2]) == std::weak_ordering::less);
166     assert(std::weak_order(v[1], v[3]) == std::weak_ordering::less);
167     assert(std::weak_order(v[1], v[4]) == std::weak_ordering::less);
168     assert(std::weak_order(v[1], v[5]) == std::weak_ordering::less);
169     assert(std::weak_order(v[1], v[6]) == std::weak_ordering::less);
170     assert(std::weak_order(v[1], v[7]) == std::weak_ordering::less);
171     assert(std::weak_order(v[1], v[8]) == std::weak_ordering::less);
172     assert(std::weak_order(v[1], v[9]) == std::weak_ordering::less);
173     assert(std::weak_order(v[1], v[10]) == std::weak_ordering::less);
174     assert(std::weak_order(v[1], v[11]) == std::weak_ordering::less);
175     assert(std::weak_order(v[1], v[12]) == std::weak_ordering::less);
176     assert(std::weak_order(v[1], v[13]) == std::weak_ordering::less);
177     assert(std::weak_order(v[2], v[0]) == std::weak_ordering::greater);
178     assert(std::weak_order(v[2], v[1]) == std::weak_ordering::greater);
179     assert(std::weak_order(v[2], v[2]) == std::weak_ordering::equivalent);
180     assert(std::weak_order(v[2], v[3]) == std::weak_ordering::less);
181     assert(std::weak_order(v[2], v[4]) == std::weak_ordering::less);
182     assert(std::weak_order(v[2], v[5]) == std::weak_ordering::less);
183     assert(std::weak_order(v[2], v[6]) == std::weak_ordering::less);
184     assert(std::weak_order(v[2], v[7]) == std::weak_ordering::less);
185     assert(std::weak_order(v[2], v[8]) == std::weak_ordering::less);
186     assert(std::weak_order(v[2], v[9]) == std::weak_ordering::less);
187     assert(std::weak_order(v[2], v[10]) == std::weak_ordering::less);
188     assert(std::weak_order(v[2], v[11]) == std::weak_ordering::less);
189     assert(std::weak_order(v[2], v[12]) == std::weak_ordering::less);
190     assert(std::weak_order(v[2], v[13]) == std::weak_ordering::less);
191     assert(std::weak_order(v[3], v[0]) == std::weak_ordering::greater);
192     assert(std::weak_order(v[3], v[1]) == std::weak_ordering::greater);
193     assert(std::weak_order(v[3], v[2]) == std::weak_ordering::greater);
194     assert(std::weak_order(v[3], v[3]) == std::weak_ordering::equivalent);
195     assert(std::weak_order(v[3], v[4]) == std::weak_ordering::less);
196     assert(std::weak_order(v[3], v[5]) == std::weak_ordering::less);
197     assert(std::weak_order(v[3], v[6]) == std::weak_ordering::less);
198     assert(std::weak_order(v[3], v[7]) == std::weak_ordering::less);
199     assert(std::weak_order(v[3], v[8]) == std::weak_ordering::less);
200     assert(std::weak_order(v[3], v[9]) == std::weak_ordering::less);
201     assert(std::weak_order(v[3], v[10]) == std::weak_ordering::less);
202     assert(std::weak_order(v[3], v[11]) == std::weak_ordering::less);
203     assert(std::weak_order(v[3], v[12]) == std::weak_ordering::less);
204     assert(std::weak_order(v[3], v[13]) == std::weak_ordering::less);
205     assert(std::weak_order(v[4], v[0]) == std::weak_ordering::greater);
206     assert(std::weak_order(v[4], v[1]) == std::weak_ordering::greater);
207     assert(std::weak_order(v[4], v[2]) == std::weak_ordering::greater);
208     assert(std::weak_order(v[4], v[3]) == std::weak_ordering::greater);
209     assert(std::weak_order(v[4], v[4]) == std::weak_ordering::equivalent);
210     assert(std::weak_order(v[4], v[5]) == std::weak_ordering::less);
211     assert(std::weak_order(v[4], v[6]) == std::weak_ordering::less);
212     assert(std::weak_order(v[4], v[7]) == std::weak_ordering::less);
213     assert(std::weak_order(v[4], v[8]) == std::weak_ordering::less);
214     assert(std::weak_order(v[4], v[9]) == std::weak_ordering::less);
215     assert(std::weak_order(v[4], v[10]) == std::weak_ordering::less);
216     assert(std::weak_order(v[4], v[11]) == std::weak_ordering::less);
217     assert(std::weak_order(v[4], v[12]) == std::weak_ordering::less);
218     assert(std::weak_order(v[4], v[13]) == std::weak_ordering::less);
219     assert(std::weak_order(v[5], v[0]) == std::weak_ordering::greater);
220     assert(std::weak_order(v[5], v[1]) == std::weak_ordering::greater);
221     assert(std::weak_order(v[5], v[2]) == std::weak_ordering::greater);
222     assert(std::weak_order(v[5], v[3]) == std::weak_ordering::greater);
223     assert(std::weak_order(v[5], v[4]) == std::weak_ordering::greater);
224     assert(std::weak_order(v[5], v[5]) == std::weak_ordering::equivalent);
225     assert(std::weak_order(v[5], v[6]) == std::weak_ordering::equivalent);
226     assert(std::weak_order(v[5], v[7]) == std::weak_ordering::less);
227     assert(std::weak_order(v[5], v[8]) == std::weak_ordering::less);
228     assert(std::weak_order(v[5], v[9]) == std::weak_ordering::less);
229     assert(std::weak_order(v[5], v[10]) == std::weak_ordering::less);
230     assert(std::weak_order(v[5], v[11]) == std::weak_ordering::less);
231     assert(std::weak_order(v[5], v[12]) == std::weak_ordering::less);
232     assert(std::weak_order(v[5], v[13]) == std::weak_ordering::less);
233     assert(std::weak_order(v[6], v[0]) == std::weak_ordering::greater);
234     assert(std::weak_order(v[6], v[1]) == std::weak_ordering::greater);
235     assert(std::weak_order(v[6], v[2]) == std::weak_ordering::greater);
236     assert(std::weak_order(v[6], v[3]) == std::weak_ordering::greater);
237     assert(std::weak_order(v[6], v[4]) == std::weak_ordering::greater);
238     assert(std::weak_order(v[6], v[5]) == std::weak_ordering::equivalent);
239     assert(std::weak_order(v[6], v[6]) == std::weak_ordering::equivalent);
240     assert(std::weak_order(v[6], v[7]) == std::weak_ordering::less);
241     assert(std::weak_order(v[6], v[8]) == std::weak_ordering::less);
242     assert(std::weak_order(v[6], v[9]) == std::weak_ordering::less);
243     assert(std::weak_order(v[6], v[10]) == std::weak_ordering::less);
244     assert(std::weak_order(v[6], v[11]) == std::weak_ordering::less);
245     assert(std::weak_order(v[6], v[12]) == std::weak_ordering::less);
246     assert(std::weak_order(v[6], v[13]) == std::weak_ordering::less);
247     assert(std::weak_order(v[7], v[0]) == std::weak_ordering::greater);
248     assert(std::weak_order(v[7], v[1]) == std::weak_ordering::greater);
249     assert(std::weak_order(v[7], v[2]) == std::weak_ordering::greater);
250     assert(std::weak_order(v[7], v[3]) == std::weak_ordering::greater);
251     assert(std::weak_order(v[7], v[4]) == std::weak_ordering::greater);
252     assert(std::weak_order(v[7], v[5]) == std::weak_ordering::greater);
253     assert(std::weak_order(v[7], v[6]) == std::weak_ordering::greater);
254     assert(std::weak_order(v[7], v[7]) == std::weak_ordering::equivalent);
255     assert(std::weak_order(v[7], v[8]) == std::weak_ordering::less);
256     assert(std::weak_order(v[7], v[9]) == std::weak_ordering::less);
257     assert(std::weak_order(v[7], v[10]) == std::weak_ordering::less);
258     assert(std::weak_order(v[7], v[11]) == std::weak_ordering::less);
259     assert(std::weak_order(v[7], v[12]) == std::weak_ordering::less);
260     assert(std::weak_order(v[7], v[13]) == std::weak_ordering::less);
261     assert(std::weak_order(v[8], v[0]) == std::weak_ordering::greater);
262     assert(std::weak_order(v[8], v[1]) == std::weak_ordering::greater);
263     assert(std::weak_order(v[8], v[2]) == std::weak_ordering::greater);
264     assert(std::weak_order(v[8], v[3]) == std::weak_ordering::greater);
265     assert(std::weak_order(v[8], v[4]) == std::weak_ordering::greater);
266     assert(std::weak_order(v[8], v[5]) == std::weak_ordering::greater);
267     assert(std::weak_order(v[8], v[6]) == std::weak_ordering::greater);
268     assert(std::weak_order(v[8], v[7]) == std::weak_ordering::greater);
269     assert(std::weak_order(v[8], v[8]) == std::weak_ordering::equivalent);
270     assert(std::weak_order(v[8], v[9]) == std::weak_ordering::less);
271     assert(std::weak_order(v[8], v[10]) == std::weak_ordering::less);
272     assert(std::weak_order(v[8], v[11]) == std::weak_ordering::less);
273     assert(std::weak_order(v[8], v[12]) == std::weak_ordering::less);
274     assert(std::weak_order(v[8], v[13]) == std::weak_ordering::less);
275     assert(std::weak_order(v[9], v[0]) == std::weak_ordering::greater);
276     assert(std::weak_order(v[9], v[1]) == std::weak_ordering::greater);
277     assert(std::weak_order(v[9], v[2]) == std::weak_ordering::greater);
278     assert(std::weak_order(v[9], v[3]) == std::weak_ordering::greater);
279     assert(std::weak_order(v[9], v[4]) == std::weak_ordering::greater);
280     assert(std::weak_order(v[9], v[5]) == std::weak_ordering::greater);
281     assert(std::weak_order(v[9], v[6]) == std::weak_ordering::greater);
282     assert(std::weak_order(v[9], v[7]) == std::weak_ordering::greater);
283     assert(std::weak_order(v[9], v[8]) == std::weak_ordering::greater);
284     assert(std::weak_order(v[9], v[9]) == std::weak_ordering::equivalent);
285     assert(std::weak_order(v[9], v[10]) == std::weak_ordering::less);
286     assert(std::weak_order(v[9], v[11]) == std::weak_ordering::less);
287     assert(std::weak_order(v[9], v[12]) == std::weak_ordering::less);
288     assert(std::weak_order(v[9], v[13]) == std::weak_ordering::less);
289     assert(std::weak_order(v[10], v[0]) == std::weak_ordering::greater);
290     assert(std::weak_order(v[10], v[1]) == std::weak_ordering::greater);
291     assert(std::weak_order(v[10], v[2]) == std::weak_ordering::greater);
292     assert(std::weak_order(v[10], v[3]) == std::weak_ordering::greater);
293     assert(std::weak_order(v[10], v[4]) == std::weak_ordering::greater);
294     assert(std::weak_order(v[10], v[5]) == std::weak_ordering::greater);
295     assert(std::weak_order(v[10], v[6]) == std::weak_ordering::greater);
296     assert(std::weak_order(v[10], v[7]) == std::weak_ordering::greater);
297     assert(std::weak_order(v[10], v[8]) == std::weak_ordering::greater);
298     assert(std::weak_order(v[10], v[9]) == std::weak_ordering::greater);
299     assert(std::weak_order(v[10], v[10]) == std::weak_ordering::equivalent);
300     assert(std::weak_order(v[10], v[11]) == std::weak_ordering::less);
301     assert(std::weak_order(v[10], v[12]) == std::weak_ordering::less);
302     assert(std::weak_order(v[10], v[13]) == std::weak_ordering::less);
303     assert(std::weak_order(v[11], v[0]) == std::weak_ordering::greater);
304     assert(std::weak_order(v[11], v[1]) == std::weak_ordering::greater);
305     assert(std::weak_order(v[11], v[2]) == std::weak_ordering::greater);
306     assert(std::weak_order(v[11], v[3]) == std::weak_ordering::greater);
307     assert(std::weak_order(v[11], v[4]) == std::weak_ordering::greater);
308     assert(std::weak_order(v[11], v[5]) == std::weak_ordering::greater);
309     assert(std::weak_order(v[11], v[6]) == std::weak_ordering::greater);
310     assert(std::weak_order(v[11], v[7]) == std::weak_ordering::greater);
311     assert(std::weak_order(v[11], v[8]) == std::weak_ordering::greater);
312     assert(std::weak_order(v[11], v[9]) == std::weak_ordering::greater);
313     assert(std::weak_order(v[11], v[10]) == std::weak_ordering::greater);
314     assert(std::weak_order(v[11], v[11]) == std::weak_ordering::equivalent);
315     assert(std::weak_order(v[11], v[12]) == std::weak_ordering::less);
316     assert(std::weak_order(v[11], v[13]) == std::weak_ordering::less);
317     assert(std::weak_order(v[12], v[0]) == std::weak_ordering::greater);
318     assert(std::weak_order(v[12], v[1]) == std::weak_ordering::greater);
319     assert(std::weak_order(v[12], v[2]) == std::weak_ordering::greater);
320     assert(std::weak_order(v[12], v[3]) == std::weak_ordering::greater);
321     assert(std::weak_order(v[12], v[4]) == std::weak_ordering::greater);
322     assert(std::weak_order(v[12], v[5]) == std::weak_ordering::greater);
323     assert(std::weak_order(v[12], v[6]) == std::weak_ordering::greater);
324     assert(std::weak_order(v[12], v[7]) == std::weak_ordering::greater);
325     assert(std::weak_order(v[12], v[8]) == std::weak_ordering::greater);
326     assert(std::weak_order(v[12], v[9]) == std::weak_ordering::greater);
327     assert(std::weak_order(v[12], v[10]) == std::weak_ordering::greater);
328     assert(std::weak_order(v[12], v[11]) == std::weak_ordering::greater);
329     assert(std::weak_order(v[12], v[12]) == std::weak_ordering::equivalent);
330     assert(std::weak_order(v[12], v[13]) == std::weak_ordering::less);
331     assert(std::weak_order(v[13], v[0]) == std::weak_ordering::greater);
332     assert(std::weak_order(v[13], v[1]) == std::weak_ordering::greater);
333     assert(std::weak_order(v[13], v[2]) == std::weak_ordering::greater);
334     assert(std::weak_order(v[13], v[3]) == std::weak_ordering::greater);
335     assert(std::weak_order(v[13], v[4]) == std::weak_ordering::greater);
336     assert(std::weak_order(v[13], v[5]) == std::weak_ordering::greater);
337     assert(std::weak_order(v[13], v[6]) == std::weak_ordering::greater);
338     assert(std::weak_order(v[13], v[7]) == std::weak_ordering::greater);
339     assert(std::weak_order(v[13], v[8]) == std::weak_ordering::greater);
340     assert(std::weak_order(v[13], v[9]) == std::weak_ordering::greater);
341     assert(std::weak_order(v[13], v[10]) == std::weak_ordering::greater);
342     assert(std::weak_order(v[13], v[11]) == std::weak_ordering::greater);
343     assert(std::weak_order(v[13], v[12]) == std::weak_ordering::greater);
344     assert(std::weak_order(v[13], v[13]) == std::weak_ordering::equivalent);
345 
346 
347     // There's no way to produce a specifically positive or negative NAN
348     // at compile-time, so the NAN-related tests must be runtime-only.
349 
350     if (!std::is_constant_evaluated()) {
351         F nq = std::copysign(std::numeric_limits<F>::quiet_NaN(), F(-1));
352         F ns = std::copysign(std::numeric_limits<F>::signaling_NaN(), F(-1));
353         F ps = std::copysign(std::numeric_limits<F>::signaling_NaN(), F(+1));
354         F pq = std::copysign(std::numeric_limits<F>::quiet_NaN(), F(+1));
355 
356         assert(std::weak_order(nq, nq) == std::weak_ordering::equivalent);
357         assert(std::weak_order(nq, ns) == std::weak_ordering::equivalent);
358         for (int i=0; i < 14; ++i) {
359             assert(std::weak_order(nq, v[i]) == std::weak_ordering::less);
360         }
361         assert(std::weak_order(nq, ps) == std::weak_ordering::less);
362         assert(std::weak_order(nq, pq) == std::weak_ordering::less);
363 
364         assert(std::weak_order(ns, nq) == std::weak_ordering::equivalent);
365         assert(std::weak_order(ns, ns) == std::weak_ordering::equivalent);
366         for (int i=0; i < 14; ++i) {
367             assert(std::weak_order(ns, v[i]) == std::weak_ordering::less);
368         }
369         assert(std::weak_order(ns, ps) == std::weak_ordering::less);
370         assert(std::weak_order(ns, pq) == std::weak_ordering::less);
371 
372         assert(std::weak_order(ps, nq) == std::weak_ordering::greater);
373         assert(std::weak_order(ps, ns) == std::weak_ordering::greater);
374         for (int i=0; i < 14; ++i) {
375             assert(std::weak_order(ps, v[i]) == std::weak_ordering::greater);
376         }
377         assert(std::weak_order(ps, ps) == std::weak_ordering::equivalent);
378         assert(std::weak_order(ps, pq) == std::weak_ordering::equivalent);
379 
380         assert(std::weak_order(pq, nq) == std::weak_ordering::greater);
381         assert(std::weak_order(pq, ns) == std::weak_ordering::greater);
382         for (int i=0; i < 14; ++i) {
383             assert(std::weak_order(pq, v[i]) == std::weak_ordering::greater);
384         }
385         assert(std::weak_order(pq, ps) == std::weak_ordering::equivalent);
386         assert(std::weak_order(pq, pq) == std::weak_ordering::equivalent);
387     }
388 
389     return true;
390 }
391 
392 namespace N14 {
393     // Compare to N12::A.
394     struct A {};
395     bool operator==(const A&, const A&);
396     constexpr std::weak_ordering operator<=>(A&, A&&) { return std::weak_ordering::less; }
397     constexpr std::weak_ordering operator<=>(A&&, A&&) { return std::weak_ordering::equivalent; }
398     std::weak_ordering operator<=>(const A&, const A&);
399     static_assert(std::three_way_comparable<A>);
400 
401     struct B {
402         std::weak_ordering operator<=>(const B&) const;  // lacks operator==
403     };
404     static_assert(!std::three_way_comparable<B>);
405 
406     struct C {
407         bool *touched;
408         bool operator==(const C&) const;
409         constexpr std::weak_ordering operator<=>(const C& rhs) const {
410             *rhs.touched = true;
411             return std::weak_ordering::equivalent;
412         }
413     };
414     static_assert(std::three_way_comparable<C>);
415 }
416 
417 constexpr bool test_1_4()
418 {
419     // Otherwise, weak_ordering(compare_three_way()(E, F)) if it is a well-formed expression.
420 
421     // Test neither weak_order nor compare_three_way const-qualify the forwarded arguments.
422     N14::A a;
423     assert(std::weak_order(a, std::move(a)) == std::weak_ordering::less);
424     assert(std::weak_order(std::move(a), std::move(a)) == std::weak_ordering::equivalent);
425 
426     N14::B b;
427     static_assert(!has_weak_order(b, b));
428 
429     // Test that the arguments are passed to <=> in the correct order.
430     bool c1_touched = false;
431     bool c2_touched = false;
432     N14::C c1 = {&c1_touched};
433     N14::C c2 = {&c2_touched};
434     assert(std::weak_order(c1, c2) == std::weak_ordering::equivalent);
435     assert(!c1_touched);
436     assert(c2_touched);
437 
438     return true;
439 }
440 
441 namespace N15 {
442     struct A {};
443     constexpr std::strong_ordering strong_order(A&, A&&) { return std::strong_ordering::less; }
444     constexpr std::strong_ordering strong_order(A&&, A&&) { return std::strong_ordering::equal; }
445     std::strong_ordering strong_order(const A&, const A&);
446 
447     struct B {
448         friend std::weak_ordering strong_order(B&, B&);
449     };
450 
451     struct WeakOrder {
452         operator std::weak_ordering() const { return std::weak_ordering::less; }
453     };
454     struct C {
455         friend WeakOrder strong_order(C& lhs, C&);
456     };
457 
458     struct StrongOrder {
459         constexpr explicit operator std::strong_ordering() const { return std::strong_ordering::less; }
460         operator std::weak_ordering() const = delete;
461     };
462     struct D {
463         bool touched = false;
464         friend constexpr StrongOrder strong_order(D& lhs, D&) { lhs.touched = true; return StrongOrder(); }
465     };
466 }
467 
468 constexpr bool test_1_5()
469 {
470     // Otherwise, weak_ordering(strong_order(E, F)) [that is, std::strong_order]
471     // if it is a well-formed expression.
472 
473     // Test that weak_order and strong_order do not const-qualify the forwarded arguments.
474     N15::A a;
475     assert(std::weak_order(a, std::move(a)) == std::weak_ordering::less);
476     assert(std::weak_order(std::move(a), std::move(a)) == std::weak_ordering::equivalent);
477 
478     // The type of ADL strong_order(e,f) must be explicitly convertible to strong_ordering
479     // (not just to weak_ordering), or else std::strong_order(e,f) won't exist.
480     N15::B b;
481     static_assert(!has_weak_order(b, b));
482 
483     // The type of ADL strong_order(e,f) must be explicitly convertible to strong_ordering
484     // (not just to weak_ordering), or else std::strong_order(e,f) won't exist.
485     N15::C c;
486     static_assert(!has_weak_order(c, c));
487 
488     N15::D d1, d2;
489     ASSERT_SAME_TYPE(decltype(std::weak_order(d1, d2)), std::weak_ordering);
490     assert(std::weak_order(d1, d2) == std::weak_ordering::less);
491     assert(d1.touched);
492     assert(!d2.touched);
493 
494     return true;
495 }
496 
497 int main(int, char**)
498 {
499     test_1_1();
500     test_1_2();
501     test_1_3<float>();
502     test_1_3<double>();
503     test_1_3<long double>();
504     test_1_4();
505     test_1_5();
506 
507     static_assert(test_1_3<float>());
508     static_assert(test_1_3<double>());
509     static_assert(test_1_3<long double>());
510     static_assert(test_1_4());
511     static_assert(test_1_5());
512 
513     return 0;
514 }
515