FTL: Standardize style
Adopt STL-flavored Google style for internal and libbase consistency.
Add README.
Bug: 160012986
Test: ftl_test
Change-Id: I1056f6fa890d68717386d634c398bb2faa46775c
diff --git a/include/ftl/static_vector.h b/include/ftl/static_vector.h
new file mode 100644
index 0000000..5012175
--- /dev/null
+++ b/include/ftl/static_vector.h
@@ -0,0 +1,396 @@
+/*
+ * 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 <ftl/array_traits.h>
+#include <ftl/initializer_list.h>
+
+#include <algorithm>
+#include <cassert>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+namespace android::ftl {
+
+constexpr struct IteratorRangeTag {} kIteratorRange;
+
+// Fixed-capacity, statically allocated counterpart of std::vector. Like std::array, StaticVector
+// allocates contiguous storage for N elements of type T at compile time, but stores at most (rather
+// than exactly) N elements. Unlike std::array, its default constructor does not require T to have a
+// default constructor, since elements are constructed in place as the vector grows. Operations that
+// insert an element (emplace_back, push_back, etc.) fail when the vector is full. The API otherwise
+// adheres to standard containers, except the unstable_erase operation that does not preserve order,
+// and the replace operation that destructively emplaces.
+//
+// StaticVector<T, 1> is analogous to an iterable std::optional.
+// StaticVector<T, 0> is an error.
+//
+// Example usage:
+//
+// ftl::StaticVector<char, 3> vector;
+// assert(vector.empty());
+//
+// vector = {'a', 'b'};
+// assert(vector.size() == 2u);
+//
+// vector.push_back('c');
+// assert(vector.full());
+//
+// assert(!vector.push_back('d'));
+// assert(vector.size() == 3u);
+//
+// vector.unstable_erase(vector.begin());
+// assert(vector == (ftl::StaticVector{'c', 'b'}));
+//
+// vector.pop_back();
+// assert(vector.back() == 'c');
+//
+// const char array[] = "hi";
+// vector = ftl::StaticVector(array);
+// assert(vector == (ftl::StaticVector{'h', 'i', '\0'}));
+//
+// ftl::StaticVector strings = ftl::init::list<std::string>("abc")
+// ("123456", 3u)
+// (3u, '?');
+// assert(strings.size() == 3u);
+// assert(strings[0] == "abc");
+// assert(strings[1] == "123");
+// assert(strings[2] == "???");
+//
+template <typename T, std::size_t N>
+class StaticVector final : ArrayTraits<T>,
+ ArrayIterators<StaticVector<T, N>, T>,
+ ArrayComparators<StaticVector> {
+ static_assert(N > 0);
+
+ using ArrayTraits<T>::construct_at;
+
+ using Iter = ArrayIterators<StaticVector, T>;
+ friend Iter;
+
+ // There is ambiguity when constructing from two iterator-like elements like pointers:
+ // they could be an iterator range, or arguments for in-place construction. Assume the
+ // latter unless they are input iterators and cannot be used to construct elements. If
+ // the former is intended, the caller can pass an IteratorRangeTag to disambiguate.
+ template <typename I, typename Traits = std::iterator_traits<I>>
+ using is_input_iterator = std::conjunction<
+ std::is_base_of<std::input_iterator_tag, typename Traits::iterator_category>,
+ std::negation<std::is_constructible<T, I>>>;
+
+public:
+ FTL_ARRAY_TRAIT(T, value_type);
+ FTL_ARRAY_TRAIT(T, size_type);
+ FTL_ARRAY_TRAIT(T, difference_type);
+
+ FTL_ARRAY_TRAIT(T, pointer);
+ FTL_ARRAY_TRAIT(T, reference);
+ FTL_ARRAY_TRAIT(T, iterator);
+ FTL_ARRAY_TRAIT(T, reverse_iterator);
+
+ FTL_ARRAY_TRAIT(T, const_pointer);
+ FTL_ARRAY_TRAIT(T, const_reference);
+ FTL_ARRAY_TRAIT(T, const_iterator);
+ FTL_ARRAY_TRAIT(T, const_reverse_iterator);
+
+ // Creates an empty vector.
+ StaticVector() = default;
+
+ // Copies and moves a vector, respectively.
+ StaticVector(const StaticVector& other)
+ : StaticVector(kIteratorRange, other.begin(), other.end()) {}
+
+ StaticVector(StaticVector&& other) { swap<true>(other); }
+
+ // Copies at most N elements from a smaller convertible vector.
+ template <typename U, std::size_t M, typename = std::enable_if_t<M <= N>>
+ StaticVector(const StaticVector<U, M>& other)
+ : StaticVector(kIteratorRange, other.begin(), other.end()) {}
+
+ // Copies at most N elements from an array.
+ template <typename U, std::size_t M>
+ explicit StaticVector(U (&array)[M])
+ : StaticVector(kIteratorRange, std::begin(array), std::end(array)) {}
+
+ // Copies at most N elements from the range [first, last).
+ //
+ // IteratorRangeTag disambiguates with initialization from two iterator-like elements.
+ //
+ template <typename Iterator, typename = std::enable_if_t<is_input_iterator<Iterator>{}>>
+ StaticVector(Iterator first, Iterator last) : StaticVector(kIteratorRange, first, last) {
+ using V = typename std::iterator_traits<Iterator>::value_type;
+ static_assert(std::is_constructible_v<value_type, V>, "Incompatible iterator range");
+ }
+
+ template <typename Iterator>
+ StaticVector(IteratorRangeTag, Iterator first, Iterator last)
+ : size_(std::min(max_size(), static_cast<size_type>(std::distance(first, last)))) {
+ std::uninitialized_copy(first, first + size_, begin());
+ }
+
+ // Constructs at most N elements. The template arguments T and N are inferred using the
+ // deduction guide defined below. Note that T is determined from the first element, and
+ // subsequent elements must have convertible types:
+ //
+ // ftl::StaticVector vector = {1, 2, 3};
+ // static_assert(std::is_same_v<decltype(vector), ftl::StaticVector<int, 3>>);
+ //
+ // const auto copy = "quince"s;
+ // auto move = "tart"s;
+ // ftl::StaticVector vector = {copy, std::move(move)};
+ //
+ // static_assert(std::is_same_v<decltype(vector), ftl::StaticVector<std::string, 2>>);
+ //
+ template <typename E, typename... Es,
+ typename = std::enable_if_t<std::is_constructible_v<value_type, E>>>
+ StaticVector(E&& element, Es&&... elements)
+ : StaticVector(std::index_sequence<0>{}, std::forward<E>(element),
+ std::forward<Es>(elements)...) {
+ static_assert(sizeof...(elements) < N, "Too many elements");
+ }
+
+ // Constructs at most N elements in place by forwarding per-element constructor arguments. The
+ // template arguments T and N are inferred using the deduction guide defined below. The syntax
+ // for listing arguments is as follows:
+ //
+ // ftl::StaticVector vector = ftl::init::list<std::string>("abc")()(3u, '?');
+ //
+ // static_assert(std::is_same_v<decltype(vector), ftl::StaticVector<std::string, 3>>);
+ // assert(vector.full());
+ // assert(vector[0] == "abc");
+ // assert(vector[1].empty());
+ // assert(vector[2] == "???");
+ //
+ template <typename U, std::size_t Size, std::size_t... Sizes, typename... Types>
+ StaticVector(InitializerList<U, std::index_sequence<Size, Sizes...>, Types...>&& list)
+ : StaticVector(std::index_sequence<0, 0, Size>{}, std::make_index_sequence<Size>{},
+ std::index_sequence<Sizes...>{}, list.tuple) {}
+
+ ~StaticVector() { std::destroy(begin(), end()); }
+
+ StaticVector& operator=(const StaticVector& other) {
+ StaticVector copy(other);
+ swap(copy);
+ return *this;
+ }
+
+ StaticVector& operator=(StaticVector&& other) {
+ std::destroy(begin(), end());
+ size_ = 0;
+ swap<true>(other);
+ return *this;
+ }
+
+ // IsEmpty enables a fast path when the vector is known to be empty at compile time.
+ template <bool IsEmpty = false>
+ void swap(StaticVector&);
+
+ static constexpr size_type max_size() { return N; }
+ size_type size() const { return size_; }
+
+ bool empty() const { return size() == 0; }
+ bool full() const { return size() == max_size(); }
+
+ iterator begin() { return std::launder(reinterpret_cast<pointer>(data_)); }
+ iterator end() { return begin() + size(); }
+
+ using Iter::begin;
+ using Iter::end;
+
+ using Iter::cbegin;
+ using Iter::cend;
+
+ using Iter::rbegin;
+ using Iter::rend;
+
+ using Iter::crbegin;
+ using Iter::crend;
+
+ using Iter::last;
+
+ using Iter::back;
+ using Iter::front;
+
+ using Iter::operator[];
+
+ // Replaces an element, and returns a reference to it. The iterator must be dereferenceable, so
+ // replacing at end() is erroneous.
+ //
+ // The element is emplaced via move constructor, so type T does not need to define copy/move
+ // assignment, e.g. its data members may be const.
+ //
+ // The arguments may directly or indirectly refer to the element being replaced.
+ //
+ // Iterators to the replaced element point to its replacement, and others remain valid.
+ //
+ template <typename... Args>
+ reference replace(const_iterator it, Args&&... args) {
+ value_type element{std::forward<Args>(args)...};
+ std::destroy_at(it);
+ // This is only safe because exceptions are disabled.
+ return *construct_at(it, std::move(element));
+ }
+
+ // Appends an element, and returns an iterator to it. If the vector is full, the element is not
+ // inserted, and the end() iterator is returned.
+ //
+ // On success, the end() iterator is invalidated.
+ //
+ template <typename... Args>
+ iterator emplace_back(Args&&... args) {
+ if (full()) return end();
+ const iterator it = construct_at(end(), std::forward<Args>(args)...);
+ ++size_;
+ return it;
+ }
+
+ // Appends an element unless the vector is full, and returns whether the element was inserted.
+ //
+ // On success, the end() iterator is invalidated.
+ //
+ bool push_back(const value_type& v) {
+ // Two statements for sequence point.
+ const iterator it = emplace_back(v);
+ return it != end();
+ }
+
+ bool push_back(value_type&& v) {
+ // Two statements for sequence point.
+ const iterator it = emplace_back(std::move(v));
+ return it != end();
+ }
+
+ // Removes the last element. The vector must not be empty, or the call is erroneous.
+ //
+ // The last() and end() iterators are invalidated.
+ //
+ void pop_back() { unstable_erase(last()); }
+
+ // Erases an element, but does not preserve order. Rather than shifting subsequent elements,
+ // this moves the last element to the slot of the erased element.
+ //
+ // The last() and end() iterators, as well as those to the erased element, are invalidated.
+ //
+ void unstable_erase(const_iterator it) {
+ std::destroy_at(it);
+ if (it != last()) {
+ // Move last element and destroy its source for destructor side effects. This is only
+ // safe because exceptions are disabled.
+ construct_at(it, std::move(back()));
+ std::destroy_at(last());
+ }
+ --size_;
+ }
+
+private:
+ // Recursion for variadic constructor.
+ template <std::size_t I, typename E, typename... Es>
+ StaticVector(std::index_sequence<I>, E&& element, Es&&... elements)
+ : StaticVector(std::index_sequence<I + 1>{}, std::forward<Es>(elements)...) {
+ construct_at(begin() + I, std::forward<E>(element));
+ }
+
+ // Base case for variadic constructor.
+ template <std::size_t I>
+ explicit StaticVector(std::index_sequence<I>) : size_(I) {}
+
+ // Recursion for in-place constructor.
+ //
+ // Construct element I by extracting its arguments from the InitializerList tuple. ArgIndex
+ // is the position of its first argument in Args, and ArgCount is the number of arguments.
+ // The Indices sequence corresponds to [0, ArgCount).
+ //
+ // The Sizes sequence lists the argument counts for elements after I, so Size is the ArgCount
+ // for the next element. The recursion stops when Sizes is empty for the last element.
+ //
+ template <std::size_t I, std::size_t ArgIndex, std::size_t ArgCount, std::size_t... Indices,
+ std::size_t Size, std::size_t... Sizes, typename... Args>
+ StaticVector(std::index_sequence<I, ArgIndex, ArgCount>, std::index_sequence<Indices...>,
+ std::index_sequence<Size, Sizes...>, std::tuple<Args...>& tuple)
+ : StaticVector(std::index_sequence<I + 1, ArgIndex + ArgCount, Size>{},
+ std::make_index_sequence<Size>{}, std::index_sequence<Sizes...>{},
+ tuple) {
+ construct_at(begin() + I, std::move(std::get<ArgIndex + Indices>(tuple))...);
+ }
+
+ // Base case for in-place constructor.
+ template <std::size_t I, std::size_t ArgIndex, std::size_t ArgCount, std::size_t... Indices,
+ typename... Args>
+ StaticVector(std::index_sequence<I, ArgIndex, ArgCount>, std::index_sequence<Indices...>,
+ std::index_sequence<>, std::tuple<Args...>& tuple)
+ : size_(I + 1) {
+ construct_at(begin() + I, std::move(std::get<ArgIndex + Indices>(tuple))...);
+ }
+
+ size_type size_ = 0;
+ std::aligned_storage_t<sizeof(value_type), alignof(value_type)> data_[N];
+};
+
+// Deduction guide for array constructor.
+template <typename T, std::size_t N>
+StaticVector(T (&)[N]) -> StaticVector<std::remove_cv_t<T>, N>;
+
+// Deduction guide for variadic constructor.
+template <typename T, typename... Us, typename V = std::decay_t<T>,
+ typename = std::enable_if_t<(std::is_constructible_v<V, Us> && ...)>>
+StaticVector(T&&, Us&&...) -> StaticVector<V, 1 + sizeof...(Us)>;
+
+// Deduction guide for in-place constructor.
+template <typename T, std::size_t... Sizes, typename... Types>
+StaticVector(InitializerList<T, std::index_sequence<Sizes...>, Types...>&&)
+ -> StaticVector<T, sizeof...(Sizes)>;
+
+template <typename T, std::size_t N>
+template <bool IsEmpty>
+void StaticVector<T, N>::swap(StaticVector& other) {
+ auto [to, from] = std::make_pair(this, &other);
+ if (from == this) return;
+
+ // Assume this vector has fewer elements, so the excess of the other vector will be moved to it.
+ auto [min, max] = std::make_pair(size(), other.size());
+
+ // No elements to swap if moving into an empty vector.
+ if constexpr (IsEmpty) {
+ assert(min == 0);
+ } else {
+ if (min > max) {
+ std::swap(from, to);
+ std::swap(min, max);
+ }
+
+ // Swap elements [0, min).
+ std::swap_ranges(begin(), begin() + min, other.begin());
+
+ // No elements to move if sizes are equal.
+ if (min == max) return;
+ }
+
+ // Move elements [min, max) and destroy their source for destructor side effects.
+ const auto [first, last] = std::make_pair(from->begin() + min, from->begin() + max);
+ std::uninitialized_move(first, last, to->begin() + min);
+ std::destroy(first, last);
+
+ std::swap(size_, other.size_);
+}
+
+template <typename T, std::size_t N>
+inline void swap(StaticVector<T, N>& lhs, StaticVector<T, N>& rhs) {
+ lhs.swap(rhs);
+}
+
+} // namespace android::ftl