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//===- iterator.h - Utilities for using and defining iterators --*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_ITERATOR_H
#define LLVM_ADT_ITERATOR_H
#include "llvm/ADT/iterator_range.h"
#include <cstddef>
#include <iterator>
#include <type_traits>
#include <utility>
namespace llvm {
/// CRTP base class which implements the entire standard iterator facade
/// in terms of a minimal subset of the interface.
///
/// Use this when it is reasonable to implement most of the iterator
/// functionality in terms of a core subset. If you need special behavior or
/// there are performance implications for this, you may want to override the
/// relevant members instead.
///
/// Note, one abstraction that this does *not* provide is implementing
/// subtraction in terms of addition by negating the difference. Negation isn't
/// always information preserving, and I can see very reasonable iterator
/// designs where this doesn't work well. It doesn't really force much added
/// boilerplate anyways.
///
/// Another abstraction that this doesn't provide is implementing increment in
/// terms of addition of one. These aren't equivalent for all iterator
/// categories, and respecting that adds a lot of complexity for little gain.
///
/// Iterators are expected to have const rules analogous to pointers, with a
/// single, const-qualified operator*() that returns ReferenceT. This matches
/// the second and third pointers in the following example:
/// \code
/// int Value;
/// { int *I = &Value; } // ReferenceT 'int&'
/// { int *const I = &Value; } // ReferenceT 'int&'; const
/// { const int *I = &Value; } // ReferenceT 'const int&'
/// { const int *const I = &Value; } // ReferenceT 'const int&'; const
/// \endcode
/// If an iterator facade returns a handle to its own state, then T (and
/// PointerT and ReferenceT) should usually be const-qualified. Otherwise, if
/// clients are expected to modify the handle itself, the field can be declared
/// mutable or use const_cast.
///
/// Classes wishing to use `iterator_facade_base` should implement the following
/// methods:
///
/// Forward Iterators:
/// (All of the following methods)
/// - DerivedT &operator=(const DerivedT &R);
/// - bool operator==(const DerivedT &R) const;
/// - T &operator*() const;
/// - DerivedT &operator++();
///
/// Bidirectional Iterators:
/// (All methods of forward iterators, plus the following)
/// - DerivedT &operator--();
///
/// Random-access Iterators:
/// (All methods of bidirectional iterators excluding the following)
/// - DerivedT &operator++();
/// - DerivedT &operator--();
/// (and plus the following)
/// - bool operator<(const DerivedT &RHS) const;
/// - DifferenceTypeT operator-(const DerivedT &R) const;
/// - DerivedT &operator+=(DifferenceTypeT N);
/// - DerivedT &operator-=(DifferenceTypeT N);
///
template <typename DerivedT, typename IteratorCategoryT, typename T,
typename DifferenceTypeT = std::ptrdiff_t, typename PointerT = T *,
typename ReferenceT = T &>
class iterator_facade_base {
public:
using iterator_category = IteratorCategoryT;
using value_type = T;
using difference_type = DifferenceTypeT;
using pointer = PointerT;
using reference = ReferenceT;
protected:
enum {
IsRandomAccess = std::is_base_of<std::random_access_iterator_tag,
IteratorCategoryT>::value,
IsBidirectional = std::is_base_of<std::bidirectional_iterator_tag,
IteratorCategoryT>::value,
};
/// A proxy object for computing a reference via indirecting a copy of an
/// iterator. This is used in APIs which need to produce a reference via
/// indirection but for which the iterator object might be a temporary. The
/// proxy preserves the iterator internally and exposes the indirected
/// reference via a conversion operator.
class ReferenceProxy {
friend iterator_facade_base;
DerivedT I;
ReferenceProxy(DerivedT I) : I(std::move(I)) {}
public:
operator ReferenceT() const { return *I; }
};
/// A proxy object for computing a pointer via indirecting a copy of a
/// reference. This is used in APIs which need to produce a pointer but for
/// which the reference might be a temporary. The proxy preserves the
/// reference internally and exposes the pointer via a arrow operator.
class PointerProxy {
friend iterator_facade_base;
ReferenceT R;
template <typename RefT>
PointerProxy(RefT &&R) : R(std::forward<RefT>(R)) {}
public:
PointerT operator->() const { return &R; }
};
public:
DerivedT operator+(DifferenceTypeT n) const {
static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
"Must pass the derived type to this template!");
static_assert(
IsRandomAccess,
"The '+' operator is only defined for random access iterators.");
DerivedT tmp = *static_cast<const DerivedT *>(this);
tmp += n;
return tmp;
}
friend DerivedT operator+(DifferenceTypeT n, const DerivedT &i) {
static_assert(
IsRandomAccess,
"The '+' operator is only defined for random access iterators.");
return i + n;
}
DerivedT operator-(DifferenceTypeT n) const {
static_assert(
IsRandomAccess,
"The '-' operator is only defined for random access iterators.");
DerivedT tmp = *static_cast<const DerivedT *>(this);
tmp -= n;
return tmp;
}
DerivedT &operator++() {
static_assert(std::is_base_of<iterator_facade_base, DerivedT>::value,
"Must pass the derived type to this template!");
return static_cast<DerivedT *>(this)->operator+=(1);
}
DerivedT operator++(int) {
DerivedT tmp = *static_cast<DerivedT *>(this);
++*static_cast<DerivedT *>(this);
return tmp;
}
DerivedT &operator--() {
static_assert(
IsBidirectional,
"The decrement operator is only defined for bidirectional iterators.");
return static_cast<DerivedT *>(this)->operator-=(1);
}
DerivedT operator--(int) {
static_assert(
IsBidirectional,
"The decrement operator is only defined for bidirectional iterators.");
DerivedT tmp = *static_cast<DerivedT *>(this);
--*static_cast<DerivedT *>(this);
return tmp;
}
#ifndef __cpp_impl_three_way_comparison
bool operator!=(const DerivedT &RHS) const {
return !(static_cast<const DerivedT &>(*this) == RHS);
}
#endif
bool operator>(const DerivedT &RHS) const {
static_assert(
IsRandomAccess,
"Relational operators are only defined for random access iterators.");
return !(static_cast<const DerivedT &>(*this) < RHS) &&
!(static_cast<const DerivedT &>(*this) == RHS);
}
bool operator<=(const DerivedT &RHS) const {
static_assert(
IsRandomAccess,
"Relational operators are only defined for random access iterators.");
return !(static_cast<const DerivedT &>(*this) > RHS);
}
bool operator>=(const DerivedT &RHS) const {
static_assert(
IsRandomAccess,
"Relational operators are only defined for random access iterators.");
return !(static_cast<const DerivedT &>(*this) < RHS);
}
PointerProxy operator->() const {
return static_cast<const DerivedT *>(this)->operator*();
}
ReferenceProxy operator[](DifferenceTypeT n) const {
static_assert(IsRandomAccess,
"Subscripting is only defined for random access iterators.");
return static_cast<const DerivedT *>(this)->operator+(n);
}
};
/// CRTP base class for adapting an iterator to a different type.
///
/// This class can be used through CRTP to adapt one iterator into another.
/// Typically this is done through providing in the derived class a custom \c
/// operator* implementation. Other methods can be overridden as well.
template <
typename DerivedT, typename WrappedIteratorT,
typename IteratorCategoryT =
typename std::iterator_traits<WrappedIteratorT>::iterator_category,
typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
typename DifferenceTypeT =
typename std::iterator_traits<WrappedIteratorT>::difference_type,
typename PointerT = std::conditional_t<
std::is_same<T, typename std::iterator_traits<
WrappedIteratorT>::value_type>::value,
typename std::iterator_traits<WrappedIteratorT>::pointer, T *>,
typename ReferenceT = std::conditional_t<
std::is_same<T, typename std::iterator_traits<
WrappedIteratorT>::value_type>::value,
typename std::iterator_traits<WrappedIteratorT>::reference, T &>>
class iterator_adaptor_base
: public iterator_facade_base<DerivedT, IteratorCategoryT, T,
DifferenceTypeT, PointerT, ReferenceT> {
using BaseT = typename iterator_adaptor_base::iterator_facade_base;
protected:
WrappedIteratorT I;
iterator_adaptor_base() = default;
explicit iterator_adaptor_base(WrappedIteratorT u) : I(std::move(u)) {
static_assert(std::is_base_of<iterator_adaptor_base, DerivedT>::value,
"Must pass the derived type to this template!");
}
const WrappedIteratorT &wrapped() const { return I; }
public:
using difference_type = DifferenceTypeT;
DerivedT &operator+=(difference_type n) {
static_assert(
BaseT::IsRandomAccess,
"The '+=' operator is only defined for random access iterators.");
I += n;
return *static_cast<DerivedT *>(this);
}
DerivedT &operator-=(difference_type n) {
static_assert(
BaseT::IsRandomAccess,
"The '-=' operator is only defined for random access iterators.");
I -= n;
return *static_cast<DerivedT *>(this);
}
using BaseT::operator-;
difference_type operator-(const DerivedT &RHS) const {
static_assert(
BaseT::IsRandomAccess,
"The '-' operator is only defined for random access iterators.");
return I - RHS.I;
}
// We have to explicitly provide ++ and -- rather than letting the facade
// forward to += because WrappedIteratorT might not support +=.
using BaseT::operator++;
DerivedT &operator++() {
++I;
return *static_cast<DerivedT *>(this);
}
using BaseT::operator--;
DerivedT &operator--() {
static_assert(
BaseT::IsBidirectional,
"The decrement operator is only defined for bidirectional iterators.");
--I;
return *static_cast<DerivedT *>(this);
}
friend bool operator==(const iterator_adaptor_base &LHS,
const iterator_adaptor_base &RHS) {
return LHS.I == RHS.I;
}
friend bool operator<(const iterator_adaptor_base &LHS,
const iterator_adaptor_base &RHS) {
static_assert(
BaseT::IsRandomAccess,
"Relational operators are only defined for random access iterators.");
return LHS.I < RHS.I;
}
ReferenceT operator*() const { return *I; }
};
/// An iterator type that allows iterating over the pointees via some
/// other iterator.
///
/// The typical usage of this is to expose a type that iterates over Ts, but
/// which is implemented with some iterator over T*s:
///
/// \code
/// using iterator = pointee_iterator<SmallVectorImpl<T *>::iterator>;
/// \endcode
template <typename WrappedIteratorT,
typename T = std::remove_reference_t<decltype(
**std::declval<WrappedIteratorT>())>>
struct pointee_iterator
: iterator_adaptor_base<
pointee_iterator<WrappedIteratorT, T>, WrappedIteratorT,
typename std::iterator_traits<WrappedIteratorT>::iterator_category,
T> {
pointee_iterator() = default;
template <typename U>
pointee_iterator(U &&u)
: pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
T &operator*() const { return **this->I; }
};
template <typename RangeT, typename WrappedIteratorT =
decltype(std::begin(std::declval<RangeT>()))>
iterator_range<pointee_iterator<WrappedIteratorT>>
make_pointee_range(RangeT &&Range) {
using PointeeIteratorT = pointee_iterator<WrappedIteratorT>;
return make_range(PointeeIteratorT(std::begin(std::forward<RangeT>(Range))),
PointeeIteratorT(std::end(std::forward<RangeT>(Range))));
}
template <typename WrappedIteratorT,
typename T = decltype(&*std::declval<WrappedIteratorT>())>
class pointer_iterator
: public iterator_adaptor_base<
pointer_iterator<WrappedIteratorT, T>, WrappedIteratorT,
typename std::iterator_traits<WrappedIteratorT>::iterator_category,
T> {
mutable T Ptr;
public:
pointer_iterator() = default;
explicit pointer_iterator(WrappedIteratorT u)
: pointer_iterator::iterator_adaptor_base(std::move(u)) {}
T &operator*() const { return Ptr = &*this->I; }
};
template <typename RangeT, typename WrappedIteratorT =
decltype(std::begin(std::declval<RangeT>()))>
iterator_range<pointer_iterator<WrappedIteratorT>>
make_pointer_range(RangeT &&Range) {
using PointerIteratorT = pointer_iterator<WrappedIteratorT>;
return make_range(PointerIteratorT(std::begin(std::forward<RangeT>(Range))),
PointerIteratorT(std::end(std::forward<RangeT>(Range))));
}
template <typename WrappedIteratorT,
typename T1 = std::remove_reference_t<decltype(
**std::declval<WrappedIteratorT>())>,
typename T2 = std::add_pointer_t<T1>>
using raw_pointer_iterator =
pointer_iterator<pointee_iterator<WrappedIteratorT, T1>, T2>;
} // end namespace llvm
#endif // LLVM_ADT_ITERATOR_H
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