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// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_BASE_ITERATOR_H_
#define V8_BASE_ITERATOR_H_
#include <iterator>
#include <tuple>
#include <utility>
namespace v8 {
namespace base {
template <class Category, class Type, class Diff = std::ptrdiff_t,
class Pointer = Type*, class Reference = Type&>
struct iterator {
using iterator_category = Category;
using value_type = Type;
using difference_type = Diff;
using pointer = Pointer;
using reference = Reference;
};
// The intention of the base::iterator_range class is to encapsulate two
// iterators so that the range defined by the iterators can be used like
// a regular STL container (actually only a subset of the full container
// functionality is available usually).
template <typename ForwardIterator>
class iterator_range {
public:
using iterator = ForwardIterator;
using const_iterator = ForwardIterator;
using pointer = typename std::iterator_traits<iterator>::pointer;
using reference = typename std::iterator_traits<iterator>::reference;
using value_type = typename std::iterator_traits<iterator>::value_type;
using difference_type =
typename std::iterator_traits<iterator>::difference_type;
iterator_range() : begin_(), end_() {}
iterator_range(ForwardIterator begin, ForwardIterator end)
: begin_(begin), end_(end) {}
iterator begin() const { return begin_; }
iterator end() const { return end_; }
const_iterator cbegin() const { return begin_; }
const_iterator cend() const { return end_; }
auto rbegin() const { return std::make_reverse_iterator(end_); }
auto rend() const { return std::make_reverse_iterator(begin_); }
bool empty() const { return cbegin() == cend(); }
// Random Access iterators only.
reference operator[](difference_type n) { return begin()[n]; }
difference_type size() const { return cend() - cbegin(); }
private:
const_iterator const begin_;
const_iterator const end_;
};
template <typename ForwardIterator>
auto make_iterator_range(ForwardIterator begin, ForwardIterator end) {
return iterator_range<ForwardIterator>{begin, end};
}
template <class T>
struct DerefPtrIterator : base::iterator<std::bidirectional_iterator_tag, T> {
T* const* ptr;
explicit DerefPtrIterator(T* const* ptr) : ptr(ptr) {}
T& operator*() const { return **ptr; }
DerefPtrIterator& operator++() {
++ptr;
return *this;
}
DerefPtrIterator& operator--() {
--ptr;
return *this;
}
bool operator!=(const DerefPtrIterator& other) const {
return ptr != other.ptr;
}
bool operator==(const DerefPtrIterator& other) const {
return ptr == other.ptr;
}
};
// {Reversed} returns a container adapter usable in a range-based "for"
// statement for iterating a reversible container in reverse order.
//
// Example:
//
// std::vector<int> v = ...;
// for (int i : base::Reversed(v)) {
// // iterates through v from back to front
// }
//
// The signature avoids binding to temporaries (T&& / const T&) on purpose. The
// lifetime of a temporary would not extend to a range-based for loop using it.
template <typename T>
auto Reversed(T& t) {
return make_iterator_range(std::rbegin(t), std::rend(t));
}
// This overload of `Reversed` is safe even when the argument is a temporary,
// because we rely on the wrapped iterators instead of the `iterator_range`
// object itself.
template <typename T>
auto Reversed(const iterator_range<T>& t) {
return make_iterator_range(std::rbegin(t), std::rend(t));
}
// {IterateWithoutLast} returns a container adapter usable in a range-based
// "for" statement for iterating all elements without the last in a forward
// order. It performs a check whether the container is empty.
//
// Example:
//
// std::vector<int> v = ...;
// for (int i : base::IterateWithoutLast(v)) {
// // iterates through v front to --back
// }
//
// The signature avoids binding to temporaries, see the remark in {Reversed}.
template <typename T>
auto IterateWithoutLast(T& t) {
DCHECK_NE(std::begin(t), std::end(t));
auto new_end = std::end(t);
return make_iterator_range(std::begin(t), --new_end);
}
template <typename T>
auto IterateWithoutLast(const iterator_range<T>& t) {
iterator_range<T> range_copy = {t.begin(), t.end()};
return IterateWithoutLast(range_copy);
}
// TupleIterator is an iterator wrapping around multiple iterators. It is use by
// the `zip` function below to iterate over multiple containers at once.
template <class... Iterators>
class TupleIterator
: public base::iterator<
std::bidirectional_iterator_tag,
std::tuple<typename std::iterator_traits<Iterators>::reference...>> {
public:
using value_type =
std::tuple<typename std::iterator_traits<Iterators>::reference...>;
explicit TupleIterator(Iterators... its) : its_(its...) {}
TupleIterator& operator++() {
std::apply([](auto&... iterators) { (++iterators, ...); }, its_);
return *this;
}
template <class Other>
bool operator!=(const Other& other) const {
return not_equal_impl(other, std::index_sequence_for<Iterators...>{});
}
value_type operator*() const {
return std::apply(
[](auto&... this_iterators) { return value_type{*this_iterators...}; },
its_);
}
private:
template <class Other, size_t... indices>
bool not_equal_impl(const Other& other,
std::index_sequence<indices...>) const {
return (... || (std::get<indices>(its_) != std::get<indices>(other.its_)));
}
std::tuple<Iterators...> its_;
};
// `zip` creates an iterator_range from multiple containers. It can be used to
// iterate over multiple containers at once. For instance:
//
// std::vector<int> arr = { 2, 4, 6 };
// std::set<double> set = { 3.5, 4.5, 5.5 };
// for (auto [i, d] : base::zip(arr, set)) {
// std::cout << i << " and " << d << std::endl;
// }
//
// Prints "2 and 3.5", "4 and 4.5" and "6 and 5.5".
template <class... Containers>
auto zip(Containers&... containers) {
using TupleIt =
TupleIterator<decltype(std::declval<Containers>().begin())...>;
return base::make_iterator_range(TupleIt(containers.begin()...),
TupleIt(containers.end()...));
}
} // namespace base
} // namespace v8
#endif // V8_BASE_ITERATOR_H_
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