1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4 * License, v. 2.0. If a copy of the MPL was not distributed with this
5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6
7 /* A polyfill for `<algorithm>`. */
8
9 #ifndef mozilla_Algorithm_h
10 #define mozilla_Algorithm_h
11
12 #include "mozilla/Result.h"
13
14 #include <iterator>
15 #include <type_traits>
16
17 namespace mozilla {
18
19 // Returns true if all elements in the range [aFirst, aLast)
20 // satisfy the predicate aPred.
21 template <class Iter, class Pred>
AllOf(Iter aFirst,Iter aLast,Pred aPred)22 constexpr bool AllOf(Iter aFirst, Iter aLast, Pred aPred) {
23 for (; aFirst != aLast; ++aFirst) {
24 if (!aPred(*aFirst)) {
25 return false;
26 }
27 }
28 return true;
29 }
30
31 // Like C++20's `std::any_of`.
32 template <typename Iter, typename Pred>
AnyOf(Iter aFirst,Iter aLast,Pred aPred)33 constexpr bool AnyOf(Iter aFirst, Iter aLast, Pred aPred) {
34 for (; aFirst != aLast; ++aFirst) {
35 if (aPred(*aFirst)) {
36 return true;
37 }
38 }
39
40 return false;
41 }
42
43 namespace detail {
44 template <typename Transform, typename SrcIter>
45 using ArrayElementTransformType = typename std::invoke_result_t<
46 Transform, typename std::iterator_traits<SrcIter>::reference>;
47
48 template <typename Transform, typename SrcIter>
49 struct TransformTraits {
50 using result_type = ArrayElementTransformType<Transform, SrcIter>;
51
52 using result_ok_type = typename result_type::ok_type;
53 using result_err_type = typename result_type::err_type;
54 };
55 } // namespace detail
56
57 // An algorithm similar to TransformAbortOnErr combined with a condition that
58 // allows to skip elements. At most std::distance(aIter, aEnd) elements will be
59 // inserted into aDst.
60 //
61 // Type requirements, in addition to those specified in TransformAbortOnErr:
62 // - Cond must be compatible with signature
63 // bool (const SrcIter::value_type&)
64 template <typename SrcIter, typename DstIter, typename Cond, typename Transform>
65 Result<Ok,
66 typename detail::TransformTraits<Transform, SrcIter>::result_err_type>
TransformIfAbortOnErr(SrcIter aIter,SrcIter aEnd,DstIter aDst,Cond aCond,Transform aTransform)67 TransformIfAbortOnErr(SrcIter aIter, SrcIter aEnd, DstIter aDst, Cond aCond,
68 Transform aTransform) {
69 for (; aIter != aEnd; ++aIter) {
70 if (!aCond(static_cast<std::add_const_t<
71 typename std::iterator_traits<SrcIter>::value_type>&>(
72 *aIter))) {
73 continue;
74 }
75
76 auto res = aTransform(*aIter);
77 if (res.isErr()) {
78 return Err(res.unwrapErr());
79 }
80
81 *aDst++ = res.unwrap();
82 }
83 return Ok{};
84 }
85
86 template <typename SrcRange, typename DstIter, typename Cond,
87 typename Transform>
TransformIfAbortOnErr(SrcRange & aRange,DstIter aDst,Cond aCond,Transform aTransform)88 auto TransformIfAbortOnErr(SrcRange& aRange, DstIter aDst, Cond aCond,
89 Transform aTransform) {
90 using std::begin;
91 using std::end;
92 return TransformIfAbortOnErr(begin(aRange), end(aRange), aDst, aCond,
93 aTransform);
94 }
95
96 // An algorithm similar to std::transform, adapted to error handling based on
97 // mozilla::Result<V, E>. It iterates through the input range [aIter, aEnd) and
98 // inserts the result of applying aTransform to each element into aDst, if
99 // aTransform returns a success result. On the first error result, iterating is
100 // aborted, and the error result is returned as an overall result. If all
101 // transformations return a success result, Ok is returned as an overall result.
102 //
103 // Type requirements:
104 // - SrcIter must be an InputIterator.
105 // - DstIter must be an OutputIterator.
106 // - Transform must be compatible with signature
107 // Result<DstIter::value_type, E> (SrcIter::reference)
108 template <typename SrcIter, typename DstIter, typename Transform>
109 Result<Ok,
110 typename detail::TransformTraits<Transform, SrcIter>::result_err_type>
TransformAbortOnErr(SrcIter aIter,SrcIter aEnd,DstIter aDst,Transform aTransform)111 TransformAbortOnErr(SrcIter aIter, SrcIter aEnd, DstIter aDst,
112 Transform aTransform) {
113 return TransformIfAbortOnErr(
114 aIter, aEnd, aDst, [](const auto&) { return true; }, aTransform);
115 }
116
117 template <typename SrcRange, typename DstIter, typename Transform>
TransformAbortOnErr(SrcRange & aRange,DstIter aDst,Transform aTransform)118 auto TransformAbortOnErr(SrcRange& aRange, DstIter aDst, Transform aTransform) {
119 using std::begin;
120 using std::end;
121 return TransformIfAbortOnErr(
122 begin(aRange), end(aRange), aDst, [](const auto&) { return true; },
123 aTransform);
124 }
125
126 } // namespace mozilla
127
128 #endif // mozilla_Algorithm_h
129