// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#ifndef CARBON_TOOLCHAIN_BASE_INDEX_BASE_H_
#define CARBON_TOOLCHAIN_BASE_INDEX_BASE_H_
#include <compare>
#include <concepts>
#include <iterator>
#include <type_traits>
#include "common/ostream.h"
#include "llvm/ADT/iterator.h"
namespace Carbon {
template <typename DataType>
class DataIterator;
// Non-templated portions of `IdBase`.
struct AnyIdBase {
 static constexpr int32_t NoneIndex = -1;
 AnyIdBase() = delete;
 constexpr explicit AnyIdBase(int index) : index(index) {}
 constexpr auto has_value() const -> bool { return index != NoneIndex; }
 int32_t index;
};
// A lightweight handle to an item identified by an opaque ID.
//
// This class is intended to be derived from by classes representing a specific
// kind of ID, whose meaning as an integer is an implementation detail of the
// type that vends the IDs. Typically this will be a vector index.
//
// Classes derived from IdBase are designed to be passed by value, not
// reference or pointer. They are also designed to be small and efficient to
// store in data structures.
//
// This uses CRTP for the `Print` function. Children should have:
// static constexpr llvm::StringLiteral Label = "my_label";
// Children can also define their own `Print` function, removing the dependency
// on `Label`.
template <typename IdT>
struct IdBase : public AnyIdBase, public Printable<idt> {
 using AnyIdBase::AnyIdBase;
 // Provide a standard `None` mapping to `NoneIndex`.
 //
 // This uses a `&` to trigger slightly different instantiation behaviors in
 // Clang. For context on why this is needed, see http://wg21.link/CWG2800.
 // NOLINTNEXTLINE(readability-identifier-naming)
 static const IdT& None;
 auto Print(llvm::raw_ostream& out) const -> void {
 out << IdT::Label; if (has_value()) { out << index; } else { out << "<none>";
 }
 }
 // Support simple equality comparison for ID types.
 friend constexpr auto operator==(IdBase<idt> lhs, IdBase<idt> rhs) -> bool {
 return lhs.index == rhs.index;
 }
};
template <typename IdT>
constexpr const IdT& IdBase<idt>::None = IdT(NoneIndex);
// A lightweight handle to an item that behaves like an index.
//
// Unlike IdBase, classes derived from IndexBase are not completely opaque, and
// provide at least an ordering between indexes that has meaning to an API
// user. Additional semantics may be specified by the derived class.
template <typename IdT>
struct IndexBase : public IdBase<idt> {
 using IdBase<idt>::IdBase;
 // Support relational comparisons for index types.
 friend auto operator<=>(IndexBase<idt> lhs, IndexBase<idt> rhs)
 -> std::strong_ordering {
 return lhs.index <=> rhs.index;
 }
};
// A random-access iterator for arrays using IndexBase-derived types.
template <typename IndexT>
class IndexIterator
 : public llvm::iterator_facade_base<indexiterator<indext>,
 std::random_access_iterator_tag,
 const IndexT, int>,
 public Printable<indexiterator<indext>> {
 public:
 IndexIterator() = delete;
 explicit IndexIterator(IndexT index) : index_(index) {}
 friend auto operator==(const IndexIterator& lhs, const IndexIterator& rhs)
 -> bool {
 return lhs.index_ == rhs.index_;
 }
 friend auto operator<=>(const IndexIterator& lhs, const IndexIterator& rhs)
 -> std::strong_ordering {
 return lhs.index_ <=> rhs.index_;
 }
 auto operator*() const -> const IndexT& { return index_; }
 using llvm::iterator_facade_base<indexiterator, std::random_access_iterator_tag, const IndexT, int>::operator-;
 friend auto operator-(const IndexIterator& lhs, const IndexIterator& rhs)
 -> int {
 return lhs.index_.index - rhs.index_.index;
 }
 auto operator+=(int n) -> IndexIterator& {
 index_.index += n;
 return *this;
 }
 auto operator-=(int n) -> IndexIterator& {
 index_.index -= n;
 return *this;
 }
 // Prints the raw token index.
 auto Print(llvm::raw_ostream& output) const -> void {
 output << index_.index;
 }
 private:
 IndexT index_;
};
} // namespace Carbon
#endif // CARBON_TOOLCHAIN_BASE_INDEX_BASE_H_
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