option-test.m

#import <Foundation/Foundation.h>

typedef NS_OPTIONS(uint32_t, SomeOption) {
    SomeOptionNone = 0,
    SomeOptionFoo = 1 << 0,
    SomeOptionBar = 1 << 1,
};

int main(int argc, char *argv[]) {
    @autoreleasepool {
        SomeOption o = SomeOptionFoo|SomeOptionBar;
        NSLog(@"o = %u", o);
    }
}

With -Wassign-enum I get a warning on line 11. I'd assumed I wouldn't get that as long as I used NS_OPTIONS.

$ clang -framework Foundation -Wassign-enum option-test.m -o option-test
option-test.m:11:24: warning: integer constant not in range of enumerated type 'SomeOption' (aka 'enum SomeOption')
      [-Wassign-enum]
        SomeOption o = SomeOptionFoo|SomeOptionBar;
                       ^
1 warning generated.

if you declare SomeOptionAll = SomeOptionFoo | SomeOptionBar as part of your options, does the warning go away?

I imagine that it ought to, as I'm assuming that the warning is really saying "that value is bigger than the biggest enum value you've declared".

It looks like NS_OPTION (and CF_OPTION) just declare the options as a typed enum, so there's no way for the compiler to know that it is valid to combine the values.

So all it could conceivably warn about is that the value of an assignment is larger than the largest enum value you defined.

It would probably require some sort of __option to be added to Clang to do more.

So it seems to be a definite this value doesn't exist in the enum list warning.

For example if we add to Simon's example:

typedef NS_OPTIONS(uint32_t, SomeOption) {
    SomeOptionNone = 0,
    SomeOptionFoo = 1 << 0,
    SomeOptionBar = 1 << 1,
    SomeOptionBaz = 1 << 2,
    SomeOptionAll = (SomeOptionBar | SomeOptionFoo | SomeOptionBaz)
};

doing:

SomeOption option = (SomeOptionBar | SomeOptionFoo | SomeOptionBaz);

is fine, while

SomeOption option = (SomeOptionBar | SomeOptionFoo);

yields the same warning as before.