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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 <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