llvm/llvm/include/llvm/ADT/SmallSet.h

//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines the SmallSet class.
///
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_SMALLSET_H
#define LLVM_ADT_SMALLSET_H

#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/type_traits.h"
#include <cstddef>
#include <functional>
#include <set>
#include <type_traits>
#include <utility>

namespace llvm {

/// SmallSetIterator - This class implements a const_iterator for SmallSet by
/// delegating to the underlying SmallVector or Set iterators.
template <typename T, unsigned N, typename C>
class SmallSetIterator
    : public iterator_facade_base<SmallSetIterator<T, N, C>,
                                  std::forward_iterator_tag, T> { … };

/// SmallSet - This maintains a set of unique values, optimizing for the case
/// when the set is small (less than N).  In this case, the set can be
/// maintained with no mallocs.  If the set gets large, we expand to using an
/// std::set to maintain reasonable lookup times.
template <typename T, unsigned N, typename C = std::less<T>>
class SmallSet {
  /// Use a SmallVector to hold the elements here (even though it will never
  /// reach its 'large' stage) to avoid calling the default ctors of elements
  /// we will never use.
  SmallVector<T, N> Vector;
  std::set<T, C> Set;

  using VIterator = typename SmallVector<T, N>::const_iterator;
  using SIterator = typename std::set<T, C>::const_iterator;
  using mutable_iterator = typename SmallVector<T, N>::iterator;

  // In small mode SmallPtrSet uses linear search for the elements, so it is
  // not a good idea to choose this value too high. You may consider using a
  // DenseSet<> instead if you expect many elements in the set.
  static_assert(N <= 32, "N should be small");

public:
  using key_type = T;
  using size_type = size_t;
  using value_type = T;
  using const_iterator = SmallSetIterator<T, N, C>;

  SmallSet() = default;

  [[nodiscard]] bool empty() const { … }

  size_type size() const { … }

  /// count - Return 1 if the element is in the set, 0 otherwise.
  size_type count(const T &V) const { … }

  /// insert - Insert an element into the set if it isn't already there.
  /// Returns a pair. The first value of it is an iterator to the inserted
  /// element or the existing element in the set. The second value is true
  /// if the element is inserted (it was not in the set before).
  std::pair<const_iterator, bool> insert(const T &V) { … }

  template <typename IterT>
  void insert(IterT I, IterT E) { … }

  bool erase(const T &V) { … }

  void clear() { … }

  const_iterator begin() const { … }

  const_iterator end() const { … }

  /// Check if the SmallSet contains the given element.
  bool contains(const T &V) const { … }

private:
  bool isSmall() const { … }

  VIterator vfind(const T &V) const { … }
};

/// If this set is of pointer values, transparently switch over to using
/// SmallPtrSet for performance.
SmallSet<PointeeType *, N>;

/// Equality comparison for SmallSet.
///
/// Iterates over elements of LHS confirming that each element is also a member
/// of RHS, and that RHS contains no additional values.
/// Equivalent to N calls to RHS.count.
/// For small-set mode amortized complexity is O(N^2)
/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
/// every hash collides).
template <typename T, unsigned LN, unsigned RN, typename C>
bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) { … }

/// Inequality comparison for SmallSet.
///
/// Equivalent to !(LHS == RHS). See operator== for performance notes.
template <typename T, unsigned LN, unsigned RN, typename C>
bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) { … }

} // end namespace llvm

#endif // LLVM_ADT_SMALLSET_H