Can't instantiate NSNumber with shorthand @n type syntax when using enum?

Question

I have an enum defined like this:

typedef enum dataTypes{
    LOW,
    MEDIUM,
    HIGH,
    MAX_DATA_TYPE
} dataTypeEnum;

I'd like to be able to instantiate an NSArray of NSNumbers like so:

NSArray * numsToUse = @[@LOW, @MEDIUM];

This is not compiling. Any insights? Do I have to go with the clunkier [NSNumber numberWithInt:] for each of these or is there a way around this? (I have considered and rejected #define statements for a number of reasons).

You should use `typedef NS_ENUM(NSInteger, DataTypeEnum) {..}` to define your enum. — orkoden, Dec 10 '15 at 16:32
@orkoden what is the difference and why is NS_ENUM preferable? — helloB, Dec 10 '15 at 17:08
[See Apple's Docs](https://developer.apple.com/library/ios/releasenotes/ObjectiveC/ModernizationObjC/AdoptingModernObjective-C/AdoptingModernObjective-C.html) tl:dr better code completion, better type information for compiler, better Swift interop — orkoden, Dec 10 '15 at 17:09

score 5 · Accepted Answer · answered Dec 10 '15 at 16:24

5

You just need to use the expression syntax:

NSArray * numsToUse = @[@(LOW), @(MEDIUM)];

answered Dec 10 '15 at 16:24

Rob Napier

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5

To add more info - the `@` syntax with no parentheses only works with number literals or `BOOL` literals. All other numeric expressions require the use of parentheses. – rmaddy Dec 10 '15 at 16:27
2

The "why" is that in parentheses the expression is evaluated and then the NSNumber boxing is applied. You can also do `@(1+1)`. – Rob Napier Dec 10 '15 at 16:39
Thanks to both of you for the clarification! – helloB Dec 10 '15 at 17:07
I want to add that the `@` syntax with no parentheses also works in front of macros that are defined to number literals. – newacct Dec 11 '15 at 01:27

Can't instantiate NSNumber with shorthand @n type syntax when using enum?

1 Answers1