AK: Find a value in any container offering iterators

Problem:
- `find` is implemented inside of each container. This coupling
  requires that each container needs to individually provide `find`.

Solution:
- Decouple the `find` functionality from the container. This allows
  provides a `find` algorithm which can work with all
  containers. Containers can still provide their own `find` in the
  case where it can be optimized.
- This also allows for searching sub-ranges of a container rather than
  the entire container as some of the container-specific member
  functions enforced.

Note:
- @davidstone's talk from 2015 C++Now conference entitled "Functions
  Want to be Free" encourages this style:
  (https://www.youtube.com/watch?v=_lVlC0xzXDc), but it does come at
  the cost of composability.
- A logical follow-on to this is to provide a mechanism to use a
  short-hand function which automatically searches the entire
  container. This could automatically use the container-provided
  version if available so that functions which provide their own
  optimized version get the benefit.

AK/Find.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Traits.h>
+#include <AK/Types.h>
+
+namespace AK {
+
+template<typename TIterator, typename TUnaryPredicate>
+constexpr TIterator find_if(TIterator first, TIterator last, TUnaryPredicate&& pred)
+{
+    for (; first != last; ++first) {
+        if (pred(*first)) {
+            return first;
+        }
+    }
+    return last;
+}
+
+template<typename TIterator, typename T>
+constexpr TIterator find(TIterator first, TIterator last, const T& value)
+{
+    return find_if(first, last, [&](const auto& v) { return Traits<T>::equals(value, v); });
+}
+
+template<typename TIterator, typename T>
+constexpr size_t find_index(TIterator first, TIterator last, const T& value)
+{
+    return find_if(first, last, [&](const auto& v) { return Traits<T>::equals(value, v); }).index();
+}
+
+}

AK/Tests/CMakeLists.txt

@@ -12,6 +12,7 @@ set(AK_TEST_SOURCES
     TestCircularQueue.cpp
     TestDistinctNumeric.cpp
     TestEndian.cpp
+    TestFind.cpp
     TestFormat.cpp
     TestHashFunctions.cpp
     TestHashMap.cpp

AK/Tests/TestFind.cpp

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2021, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/TestSuite.h>
+
+#include <AK/Array.h>
+#include <AK/Find.h>
+#include <AK/Vector.h>
+
+TEST_CASE(should_return_end_if_not_in_container)
+{
+    constexpr AK::Array<int, 10> a {};
+
+    static_assert(a.end() == AK::find(a.begin(), a.end(), 1));
+
+    EXPECT(a.end() == AK::find(a.begin(), a.end(), 1));
+}
+
+TEST_CASE(should_return_iterator_to_first_matching_value_in_container)
+{
+    static constexpr AK::Array<int, 10> a { 1, 2, 3, 4, 0, 6, 7, 8, 0, 0 };
+
+    constexpr auto expected = a.begin() + 4;
+
+    static_assert(expected == AK::find(a.begin(), a.end(), 0));
+
+    EXPECT(expected == AK::find(a.begin(), a.end(), 0));
+}
+
+TEST_CASE(should_return_iterator_to_first_predicate_matching_value_in_container)
+{
+    static constexpr AK::Array<int, 10> a { 1, 2, 3, 4, 0, 6, 7, 8, 0, 0 };
+
+    constexpr auto expected = a.begin() + 4;
+
+    static_assert(expected == AK::find_if(a.begin(), a.end(), [](auto v) { return v == 0; }));
+
+    EXPECT(expected == AK::find_if(a.begin(), a.end(), [](auto v) { return v == 0; }));
+
+    auto find_me = 8;
+    EXPECT(find_me == *AK::find_if(a.begin(), a.end(), [&](auto v) { return v == find_me; }));
+}
+
+TEST_CASE(should_return_index_to_first_predicate_matching_value_in_container)
+{
+    static constexpr AK::Array<int, 10> a { 1, 2, 3, 4, 0, 6, 7, 8, 0, 0 };
+
+    static_assert(4 == AK::find_index(a.begin(), a.end(), 0));
+
+    EXPECT(4 == AK::find_index(a.begin(), a.end(), 0));
+}
+
+TEST_MAIN(Find)

AK/Traits.h

@@ -35,7 +35,7 @@ template<typename T>
 struct GenericTraits {
     using PeekType = T;
     static constexpr bool is_trivial() { return false; }
-    static bool equals(const T& a, const T& b) { return a == b; }
+    static constexpr bool equals(const T& a, const T& b) { return a == b; }
 };
 
 template<typename T>