Modern C++ Bitmask types
Bitmask flags are a ubiquitous pattern in C & C++ code. In the ‘old days’, they were typically defined as:
#define FLAGS_NONE 0x0
#define FLAGS_DO_A_THING 0x1
#define FLAGS_DISABLE_A_THING 0x2
#define FLAGS_OPTIONAL_FEATURE 0x4
HRESULT MyFunction(int flags);
Since C/C++ preprocessor defines tend to have a lot of potential hazards, over time developers have moved to using enum:
enum FLAGS_FOR_MYFUNCTION
{
FLAGS_NONE = 0x0,
FLAGS_DO_A_THING = 0x1,
FLAGS_DISABLE_A_THING = 0x2,
FLAGS_OPTIONAL_FEATURE = 0x4
};
HRESULT MyFunction(int flags);
With C++11 you can also provide an underlying type of the enum so you can use unsigned long instead of int without any signed/unsigned mismatch warnings:
enum FLAGS_FOR_MYFUNCTION : unsigned long
{
FLAGS_NONE = 0x0,
FLAGS_DO_A_THING = 0x1,
FLAGS_DISABLE_A_THING = 0x2,
FLAGS_OPTIONAL_FEATURE = 0x4
};
HRESULT MyFunction(unsigned long flags);
This still leaves the use of flags ‘loosely typed’ since if you had a second set of (possibly unrelated) flags you can easily write:
HRESULT MyFunction(FLAGS_DO_A_THING | UNRELATED_FLAGS_FEATURE);
Modern C++ recommends solving this with Bitmask flags per the standard (section 17.5.2.1.13). DirectX 11 used the older loosely typed DWORD (a.k.a unsigned long) plus enum flags, but DirectX 12 adopts this new typed bitmask flags pattern. Therefore, I’ve updated my GitHub libraries to use the pattern as well, and this does have some implications for existing code.