On Wednesday, January 25, 2012 03:22:03 Trass3r wrote: > So I was just reading > http://stackoverflow.com/questions/1448396/how-to-use-enums-as-flags-in-c > > And did a quick test: > > enum STC > { > A = 0x1, > B = 0x2, > C = 0x4 > } > enum FOO > { > F = 0x8, > G = 0x10 > } > > void main() > { > STC s = STC.A | STC.C; > STC s2 = s & STC.A; > auto s2_2 = s & STC.A; > static assert(is(typeof(s2_2) == STC)); > > static assert(!__traits(compiles, { if (s & FOO.F) {} })); // > fails. that one's hard to track down > static assert(!__traits(compiles, { auto s3 = s & FOO.F; })); // > fails, cause implicitly converts to int > static assert(!__traits(compiles, { STC s4 = s & FOO.F; })); > static assert(!__traits(compiles, { FOO s5 = s & FOO.F; })); > > static assert(!__traits(compiles, { STC t = STC.A | FOO.F; })); > static assert(!__traits(compiles, { auto t = STC.A | FOO.F; })); // > fails > > static assert(!__traits(compiles, { if (s & STC.B == 0) {} })); // > works, but error not gagged > static assert(!__traits(compiles, { if (s && STC.B) {} })); // > fails > } > > Does it really make sense to allow bitwise operations on different enums? > There should at least be some way to get this straight without having to > resort to a heap of code like in C++: > http://www.artima.com/cppsource/safelabels.html
I think that it makes sense to use enums as flags, but I do _not_ think that it makes sense to use an enum as the type of the variable _holding_ the flags. STC var = STC.A & STC.B; is an abimination IMHO. adding another enum to the list and doing something like STC var = STC.A & FOO.F; just makes it worse. It should be something like uint var = STC.A & FOO.F; instead. Now anding two different enums like that is still a bit weird, but I don't know that it should really be illegal. It's assigning anded enums to an enum that I want to see die. I'd _love_ it if that were illegal. For instance, std.socket uses flag enums, which is fine, but in some places it uses them as the type of function parameters, which is _not_ a good idea IMHO. Whenever I think about it, I keep meaning to go and fix it, but I never get around to it. - Jonathan M Davis
