16 Library introduction [library]

16.3 Method of description [description]

16.3.3 Other conventions [conventions]

16.3.3.3 Type descriptions [type.descriptions]

16.3.3.3.4 Bitmask types [bitmask.types]

Several types defined in [support] through [thread] and [depr] are bitmask types.
Each bitmask type can be implemented as an enumerated type that overloads certain operators, as an integer type, or as a bitset.
The bitmask type bitmask can be written: // For exposition only. // int_­type is an integral type capable of representing all values of the bitmask type. enum bitmask : int_type { = 1 << 0, = 1 << 1, = 1 << 2, = 1 << 3, }; inline constexpr (); inline constexpr (); inline constexpr (); inline constexpr (); ⋮ constexpr bitmask operator&(bitmask X, bitmask Y) { return static_cast<bitmask>( static_cast<int_type>(X) & static_cast<int_type>(Y)); } constexpr bitmask operator|(bitmask X, bitmask Y) { return static_cast<bitmask>( static_cast<int_type>(X) | static_cast<int_type>(Y)); } constexpr bitmask operator^(bitmask X, bitmask Y) { return static_cast<bitmask>( static_cast<int_type>(X) ^ static_cast<int_type>(Y)); } constexpr bitmask operator~(bitmask X) { return static_cast<bitmask>(~static_cast<int_type>(X)); } bitmask& operator&=(bitmask& X, bitmask Y) { X = X & Y; return X; } bitmask& operator|=(bitmask& X, bitmask Y) { X = X | Y; return X; } bitmask& operator^=(bitmask& X, bitmask Y) { X = X ^ Y; return X; }
Here, the names , , etc. represent bitmask elements for this particular bitmask type.
All such elements have distinct, nonzero values such that, for any pair and where , & is nonzero and & is zero.
Additionally, the value 0 is used to represent an empty bitmask, in which no bitmask elements are set.
The following terms apply to objects and values of bitmask types:
  • To set a value Y in an object X is to evaluate the expression X |= Y.
  • To clear a value Y in an object X is to evaluate the expression X &= ~Y.
  • The value Y is set in the object X if the expression X & Y is nonzero.