1 files changed, 135 insertions, 0 deletions
diff --git a/include/ftl/array_traits.h b/include/ftl/array_traits.h
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+++ b/include/ftl/array_traits.h
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+/*
+ * Copyright 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <algorithm>
+#include <iterator>
+#include <new>
+#include <type_traits>
+
+#define FTL_ARRAY_TRAIT(T, U) using U = typename ArrayTraits<T>::U
+
+namespace android::ftl {
+
+template <typename T>
+struct ArrayTraits {
+  using value_type = T;
+  using size_type = std::size_t;
+  using difference_type = std::ptrdiff_t;
+
+  using pointer = value_type*;
+  using reference = value_type&;
+  using iterator = pointer;
+  using reverse_iterator = std::reverse_iterator<iterator>;
+
+  using const_pointer = const value_type*;
+  using const_reference = const value_type&;
+  using const_iterator = const_pointer;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+  template <typename... Args>
+  static pointer construct_at(const_iterator it, Args&&... args) {
+    void* const ptr = const_cast<void*>(static_cast<const void*>(it));
+    if constexpr (std::is_constructible_v<value_type, Args...>) {
+      // TODO: Replace with std::construct_at in C++20.
+      return new (ptr) value_type(std::forward<Args>(args)...);
+    } else {
+      // Fall back to list initialization.
+      return new (ptr) value_type{std::forward<Args>(args)...};
+    }
+  }
+};
+
+// CRTP mixin to define iterator functions in terms of non-const Self::begin and Self::end.
+template <typename Self, typename T>
+class ArrayIterators {
+  FTL_ARRAY_TRAIT(T, size_type);
+
+  FTL_ARRAY_TRAIT(T, reference);
+  FTL_ARRAY_TRAIT(T, iterator);
+  FTL_ARRAY_TRAIT(T, reverse_iterator);
+
+  FTL_ARRAY_TRAIT(T, const_reference);
+  FTL_ARRAY_TRAIT(T, const_iterator);
+  FTL_ARRAY_TRAIT(T, const_reverse_iterator);
+
+  Self& self() const { return *const_cast<Self*>(static_cast<const Self*>(this)); }
+
+ public:
+  const_iterator begin() const { return cbegin(); }
+  const_iterator cbegin() const { return self().begin(); }
+
+  const_iterator end() const { return cend(); }
+  const_iterator cend() const { return self().end(); }
+
+  reverse_iterator rbegin() { return std::make_reverse_iterator(self().end()); }
+  const_reverse_iterator rbegin() const { return crbegin(); }
+  const_reverse_iterator crbegin() const { return self().rbegin(); }
+
+  reverse_iterator rend() { return std::make_reverse_iterator(self().begin()); }
+  const_reverse_iterator rend() const { return crend(); }
+  const_reverse_iterator crend() const { return self().rend(); }
+
+  iterator last() { return self().end() - 1; }
+  const_iterator last() const { return self().last(); }
+
+  reference front() { return *self().begin(); }
+  const_reference front() const { return self().front(); }
+
+  reference back() { return *last(); }
+  const_reference back() const { return self().back(); }
+
+  reference operator[](size_type i) { return *(self().begin() + i); }
+  const_reference operator[](size_type i) const { return self()[i]; }
+};
+
+// Mixin to define comparison operators for an array-like template.
+// TODO: Replace with operator<=> in C++20.
+template <template <typename, std::size_t> class Array>
+struct ArrayComparators {
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator==(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return lhs.size() == rhs.size() && std::equal(lhs.begin(), lhs.end(), rhs.begin());
+  }
+
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator<(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
+  }
+
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator>(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return rhs < lhs;
+  }
+
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator!=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return !(lhs == rhs);
+  }
+
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator>=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return !(lhs < rhs);
+  }
+
+  template <typename T, std::size_t N, std::size_t M>
+  friend bool operator<=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
+    return !(lhs > rhs);
+  }
+};
+
+}  // namespace android::ftl