Add Flags<T> class as a type-safe way of storing OR-combinations of enums.

src/base/flags.h

+// 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_FLAGS_H_
+#define V8_BASE_FLAGS_H_
+
+#include "include/v8config.h"
+
+namespace v8 {
+namespace base {
+
+// The Flags class provides a type-safe way of storing OR-combinations of enum
+// values. The Flags<T> class is a template class, where T is an enum type.
+//
+// The traditional C++ approach for storing OR-combinations of enum values is to
+// use an int or unsigned int variable. The inconvenience with this approach is
+// that there's no type checking at all; any enum value can be OR'd with any
+// other enum value and passed on to a function that takes an int or unsigned
+// int.
+template <typename T>
+class Flags V8_FINAL {
+ public:
+  typedef T flag_type;
+  typedef int mask_type;
+
+  Flags() : mask_(0) {}
+  Flags(flag_type flag) : mask_(flag) {}  // NOLINT(runtime/explicit)
+  explicit Flags(mask_type mask) : mask_(mask) {}
+  Flags(const Flags& flags) : mask_(flags.mask_) {}

[Sven Panne, 2014/08/27 12:15:02]

Do we really need an explicit copy constructor and assignment operator? They are
equivalent to the auto-generated ones.

+  Flags& operator=(const Flags& flags) {
+    mask_ = flags.mask_;
+    return *this;
+  }
+
+  Flags& operator&=(const Flags& flags) {
+    mask_ &= flags.mask_;
+    return *this;
+  }
+  Flags& operator|=(const Flags& flags) {
+    mask_ |= flags.mask_;
+    return *this;
+  }
+  Flags& operator^=(const Flags& flags) {
+    mask_ ^= flags.mask_;
+    return *this;
+  }
+
+  Flags operator&(const Flags& flags) const { return Flags(*this) &= flags; }
+  Flags operator|(const Flags& flags) const { return Flags(*this) |= flags; }
+  Flags operator^(const Flags& flags) const { return Flags(*this) ^= flags; }
+
+  Flags& operator&=(flag_type flag) { return operator&=(Flags(flag)); }
+  Flags& operator|=(flag_type flag) { return operator|=(Flags(flag)); }
+  Flags& operator^=(flag_type flag) { return operator^=(Flags(flag)); }
+
+  Flags operator&(flag_type flag) const { return operator&(Flags(flag)); }
+  Flags operator|(flag_type flag) const { return operator|(Flags(flag)); }
+  Flags operator^(flag_type flag) const { return operator^(Flags(flag)); }
+
+  Flags operator~() const { return Flags(~mask_); }
+
+  operator mask_type() const { return mask_; }
+  bool operator!() const { return !mask_; }
+
+ private:
+  mask_type mask_;
+};
+
+
+#define DEFINE_FLAGS(Type, Enum) typedef ::v8::base::Flags<Enum> Type
+
+#define DEFINE_OPERATORS_FOR_FLAGS(Type)                                       \
+  inline ::v8::base::Flags<Type::flag_type> operator&(                         \
+      Type::flag_type lhs,                                                     \
+      Type::flag_type rhs)V8_UNUSED V8_WARN_UNUSED_RESULT;                     \
+  inline ::v8::base::Flags<Type::flag_type> operator&(Type::flag_type lhs,     \
+                                                      Type::flag_type rhs) {   \
+    return ::v8::base::Flags<Type::flag_type>(lhs) & rhs;                      \
+  }                                                                            \
+  inline ::v8::base::Flags<Type::flag_type> operator&(                         \
+      Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs)      \
+      V8_UNUSED V8_WARN_UNUSED_RESULT;                                         \
+  inline ::v8::base::Flags<Type::flag_type> operator&(                         \
+      Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs) {    \
+    return rhs & lhs;                                                          \
+  }                                                                            \
+  inline void operator&(Type::flag_type lhs, Type::mask_type rhs)V8_UNUSED;    \
+  inline void operator&(Type::flag_type lhs, Type::mask_type rhs) {}           \
+  inline ::v8::base::Flags<Type::flag_type> operator|(Type::flag_type lhs,     \
+                                                      Type::flag_type rhs)     \
+      V8_UNUSED V8_WARN_UNUSED_RESULT;                                         \
+  inline ::v8::base::Flags<Type::flag_type> operator|(Type::flag_type lhs,     \
+                                                      Type::flag_type rhs) {   \
+    return ::v8::base::Flags<Type::flag_type>(lhs) | rhs;                      \
+  }                                                                            \
+  inline ::v8::base::Flags<Type::flag_type> operator|(                         \
+      Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs)      \
+      V8_UNUSED V8_WARN_UNUSED_RESULT;                                         \
+  inline ::v8::base::Flags<Type::flag_type> operator|(                         \
+      Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs) {    \
+    return rhs | lhs;                                                          \
+  }                                                                            \
+  inline void operator|(Type::flag_type lhs, Type::mask_type rhs) V8_UNUSED;   \
+  inline void operator|(Type::flag_type lhs, Type::mask_type rhs) {}           \
+  inline ::v8::base::Flags<Type::flag_type> operator^(Type::flag_type lhs,     \
+                                                      Type::flag_type rhs)     \
+      V8_UNUSED V8_WARN_UNUSED_RESULT;                                         \
+  inline ::v8::base::Flags<Type::flag_type> operator^(Type::flag_type lhs,     \
+                                                      Type::flag_type rhs) {   \
+    return ::v8::base::Flags<Type::flag_type>(lhs) ^ rhs;                      \
+  } inline ::v8::base::Flags<Type::flag_type>                                  \
+      operator^(Type::flag_type lhs,                                           \
+                const ::v8::base::Flags<Type::flag_type>& rhs)                 \
+      V8_UNUSED V8_WARN_UNUSED_RESULT;                                         \
+  inline ::v8::base::Flags<Type::flag_type> operator^(                         \
+      Type::flag_type lhs, const ::v8::base::Flags<Type::flag_type>& rhs) {    \
+    return rhs ^ lhs;                                                          \
+  } inline void operator^(Type::flag_type lhs, Type::mask_type rhs) V8_UNUSED; \
+  inline void operator^(Type::flag_type lhs, Type::mask_type rhs) {}
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_BASE_FLAGS_H_