[PATCH V2] wayland.xml: add "enum", "bitfield" and "is_bitfield" attributes
spitzak at gmail.com
Tue Sep 23 11:43:08 PDT 2014
On 09/23/2014 08:17 AM, Nils Chr. Brause wrote:
> more than the power-of-two values listed isn't a problem in my opinion. I see
> these extra values as some sort of shortcuts for often used OR-combinations.
That is what I was thinking too. A bitfield can be treated identically
to an enum. I think there may be confusion that the values would be
specified differently. But they should be specified as the actual
numeric power of 2 that the resulting integer has, and extra values that
are not powers of 2 are allowed. This means that a backend that does not
distinguish enum and bitfield can trivially treat them the same.
Backends that do care will look for the entries that are powers of 2 and
use them as the bits. Depending on the language they may be able to do
something with the other values (certainly C++ could handle those
easily, though it gets tricky if you want to prevent & with these values).
In C++11 this just means adding an inline operator| and operator& to the
enum in the header file. Pre-C++11 you have to make a fake class which
If the bitfield is missing the best that can be done is to assume all
enums are bitfields. This will allow invalid settings that could be
detected at compile time to be passed to the ones that are not bitfields.
So I certainly see some advantage in this and no harm whatsoever.
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