Unpacking packed primitives (such as an enum) from NSArray or NSDictionary during fast enumeration

Question

You can put primitives in an NSArray or NSDictionary by packing them with the @() syntax. For example:

typedef enum {
    MyEnumOne,
    MyEnumTwo
} MyEnum

NSDictionary *dictionary = @{
                             @(MyEnumOne) : @"one",
                             @(MyEnumTwo) : @"two"
                             };

But how do you then use this with fast enumeration? For example, something like:

for (MyEnum enum in dictionary) {
    ...
}

This results in the error Selector element type 'MyEnum' is not a valid object

score 1 · Answer 1 · answered Feb 21 '15 at 01:57

The @() syntax creates a boxed NSNumber. Therefore, when enumerating, access it as an NSNumber. To cast it back to an enum, first extract the integer value, then cast:

for (NSNumber *number in dictionary) {
    MyEnum myEnum = (MyEnum)[number intValue];
    ...
}

Unpacking packed primitives (such as an enum) from NSArray or NSDictionary during fast enumeration

1 Answers1