sousa-gecko/mfbt/EnumeratedRange.h

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* Iterator over contiguous enum values */

/*
 * Implements generator functions that create a range to iterate over the values
 * of a scoped or unscoped enum. Unlike IntegerRange, which can only function on
 * the underlying integral type, the elements of the generated sequence will
 * have the type of the enum in question.
 *
 * Note that the enum values should be contiguous in the iterated range;
 * unfortunately there exists no way for EnumeratedRange to enforce this
 * either dynamically or at compile time.
 */

#ifndef mozilla_EnumeratedRange_h
#define mozilla_EnumeratedRange_h

#include <type_traits>

#include "mozilla/Assertions.h"
#include "mozilla/ReverseIterator.h"

#ifdef DEBUG
#  include <limits>
#endif

namespace mozilla {

namespace detail {

template <typename EnumTypeT>
class EnumeratedIterator {
 public:
  typedef std::underlying_type_t<EnumTypeT> IntTypeT;

  template <typename EnumType>
  constexpr explicit EnumeratedIterator(EnumType aCurrent)
      : mCurrent(aCurrent) {}

  template <typename EnumType>
  explicit EnumeratedIterator(const EnumeratedIterator<EnumType>& aOther)
      : mCurrent(aOther.mCurrent) {}

  EnumTypeT operator*() const { return mCurrent; }

  /* Increment and decrement operators */

  EnumeratedIterator& operator++() {
    mCurrent = EnumTypeT(IntTypeT(mCurrent) + IntTypeT(1));
    return *this;
  }
  EnumeratedIterator& operator--() {
    mCurrent = EnumTypeT(IntTypeT(mCurrent) - IntTypeT(1));
    return *this;
  }
  EnumeratedIterator operator++(int) {
    auto ret = *this;
    mCurrent = EnumTypeT(IntTypeT(mCurrent) + IntTypeT(1));
    return ret;
  }
  EnumeratedIterator operator--(int) {
    auto ret = *this;
    mCurrent = EnumTypeT(IntTypeT(mCurrent) - IntTypeT(1));
    return ret;
  }

  /* Comparison operators */

  friend bool operator==(const EnumeratedIterator<EnumTypeT>& aIter1,
                         const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent == aIter2.mCurrent;
  }

  friend bool operator!=(const EnumeratedIterator<EnumTypeT>& aIter1,
                         const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent != aIter2.mCurrent;
  }

  friend bool operator<(const EnumeratedIterator<EnumTypeT>& aIter1,
                        const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent < aIter2.mCurrent;
  }

  friend bool operator<=(const EnumeratedIterator<EnumTypeT>& aIter1,
                         const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent <= aIter2.mCurrent;
  }
  friend bool operator>(const EnumeratedIterator<EnumTypeT>& aIter1,
                        const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent > aIter2.mCurrent;
  }
  friend bool operator>=(const EnumeratedIterator<EnumTypeT>& aIter1,
                         const EnumeratedIterator<EnumTypeT>& aIter2) {
    return aIter1.mCurrent >= aIter2.mCurrent;
  }

 private:
  EnumTypeT mCurrent;
};

template <typename EnumTypeT>
class EnumeratedRange {
 public:
  typedef EnumeratedIterator<EnumTypeT> iterator;
  typedef EnumeratedIterator<EnumTypeT> const_iterator;
  typedef ReverseIterator<iterator> reverse_iterator;
  typedef ReverseIterator<const_iterator> const_reverse_iterator;

  template <typename EnumType>
  constexpr EnumeratedRange(EnumType aBegin, EnumType aEnd)
      : mBegin(aBegin), mEnd(aEnd) {}

  iterator begin() const { return iterator(mBegin); }
  const_iterator cbegin() const { return begin(); }
  iterator end() const { return iterator(mEnd); }
  const_iterator cend() const { return end(); }
  reverse_iterator rbegin() const { return reverse_iterator(mEnd); }
  const_reverse_iterator crbegin() const { return rbegin(); }
  reverse_iterator rend() const { return reverse_iterator(mBegin); }
  const_reverse_iterator crend() const { return rend(); }

 private:
  EnumTypeT mBegin;
  EnumTypeT mEnd;
};

}  // namespace detail

#ifdef __GNUC__
// Enums can have an unsigned underlying type, which makes some of the
// comparisons below always true or always false. Temporarily disable
// -Wtype-limits to avoid breaking -Werror builds.
#  pragma GCC diagnostic push
#  pragma GCC diagnostic ignored "-Wtype-limits"
#endif

// Create a range to iterate from aBegin to aEnd, exclusive.
template <typename EnumType>
constexpr detail::EnumeratedRange<EnumType> MakeEnumeratedRange(EnumType aBegin,
                                                                EnumType aEnd) {
  MOZ_ASSERT(aBegin <= aEnd, "Cannot generate invalid, unbounded range!");
  return detail::EnumeratedRange<EnumType>(aBegin, aEnd);
}

// Create a range to iterate from EnumType(0) to aEnd, exclusive. EnumType(0)
// should exist, but note that there is no way for us to ensure that it does!
template <typename EnumType>
constexpr detail::EnumeratedRange<EnumType> MakeEnumeratedRange(EnumType aEnd) {
  return MakeEnumeratedRange(EnumType(0), aEnd);
}

// Create a range to iterate from aBegin to aEnd, inclusive.
//
// NOTE: This internally constructs a value that is one past `aEnd`, so the
// enumeration needs to either have a fixed underlying type, or `aEnd + 1` must
// be inside the range of the enumeration, in order to not be undefined
// behavior.
//
// See bug 1614512.
template <typename EnumType>
constexpr detail::EnumeratedRange<EnumType> MakeInclusiveEnumeratedRange(
    EnumType aBegin, EnumType aEnd) {
  using EnumUnderlyingType = std::underlying_type_t<EnumType>;
  const auto end = static_cast<EnumUnderlyingType>(aEnd);

  MOZ_ASSERT(end != std::numeric_limits<EnumUnderlyingType>::max(),
             "aEnd shouldn't overflow!");
  return MakeEnumeratedRange(aBegin, static_cast<EnumType>(end + 1));
}

template <typename EnumType>
constexpr auto MakeInclusiveEnumeratedRange(EnumType aEnd) {
  return MakeInclusiveEnumeratedRange(EnumType{0}, aEnd);
}

#ifdef __GNUC__
#  pragma GCC diagnostic pop
#endif

}  // namespace mozilla

#endif  // mozilla_EnumeratedRange_h