Today I landed bug 1371771 [1] (on inbound at the time of writing
this), which adds a new MOZ_DEFINE_ENUM macro to MFBT.
This macro defines an enumeration, together with a constant that
stores the number of enumerators (and, in addition, another constant
that stores the highest enumerator).
For example,
MOZ_DEFINE_ENUM(Foo, (A, B, C));
will expand to:
enum Foo { A, B, C };
constexpr size_t kFooCount = 3;
constexpr Foo kHighestFoo = Foo(kFooCount - 1);
This avoids having to give your enumeration a "sentinel" value for
purposes such as IPC serialization (since you can just use the
constant generated by the macro instead), which in turn means you
don't need special handling for a sentinel value in switch statements
and such.
There are also some variants of the macro to support use cases such as
enum classes, enums with a specified underlying type, and enums at
class scope. See the documentation in mfbt/DefineEnum.h for more
details and motivation.
Consider using MOZ_DEFINE_ENUM instead of a sentinel enumerator in
newly added enumerations, and, if you're so inclined, consider
refactoring existing enumerations to use MOZ_DEFINE_ENUM instead of a
sentinel (I've already done so for enumerations in gfx/layers in bug
1377020 [2]).
Cheers,
Botond
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1371771
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1377020
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