@class for typedef enum?

Question

In one header file, I have something like:

// PasscodeInputViewController.h

typedef enum {
    PasscodeInputModeOn,     // set passcode
    PasscodeInputModeEnter,  // enter passcode
    PasscodeInputModeChange, // change passcode
    PasscodeInputModeOff     // turn off passcode
} PasscodeInputMode;

In another header file, I declare a method that takes an argument of type PasscodeInputMode:

#import "PasscodeInputViewController.h"

- (void)presentPasscodeInputWithMode:(PasscodeInputMode)mode;

As you can see, I use #import "PasscodeInputViewController.h" as above so that PasscodeInputMode is recognized, but is there a @class equivalent for typedef enum?

@Inder Kumar Rathore, well for class names you're supposed to use `@class` in the header file & `#import` in the .m file. I'm wondering if there's something analogous to `@class` for `typedef enum`s. — ma11hew28, May 06 '11 at 14:49
Swift adds a wrinkle. An include in a header may generate the error "include of non-modular header inside framework module". The solution is to move the header into the .m and use @class to forward declare anything missing. But for enums, there's apparently no way to do that. Suggestions? — David Gish, Dec 19 '15 at 05:46
@ma11hew28, Forward declaring enums: https://stackoverflow.com/a/42073674/342794 — lal, Sep 21 '17 at 17:41

score 14 · Accepted Answer · answered May 06 '11 at 04:09

14

No, there isn’t an equivalent.

Enumerations in Objective-C are the same as enumerations in C. Since the underlying type of an enumeration is implementation-dependent (e.g., it could be char or int), the compiler must know the complete declaration of the enumeration.

That said, a type specifier

enum nameOfEnum

without listing the enumeration members is valid C provided it appears after the type it specifies is complete, i.e., enum nameOfEnum { … } must appear beforehand in the translation unit.

In summary: There’s no forward declaration of enumerations, only backward references.

answered May 06 '11 at 04:09

Thanks!. So, then, I should just stick with the `#import`? – ma11hew28 May 06 '11 at 14:47
1

@Matt Yup. There’s nothing else you can do, really. – May 06 '11 at 20:46
@Bavarious I heard that ObjectiveC now takes advantages of C++11 also, so it supports fixed type enum ? – onmyway133 Jan 20 '14 at 03:56
@Bavarious, new way to forward declare enums: https://stackoverflow.com/questions/946489/forward-declare-enum-in-objective-c?s=1|4.0538 – lal Sep 21 '17 at 17:46

lal · Answer 2 · 2017-12-16T18:22:00.527

@Caleb, @Bavarious:

Most recent way (Jan, 2017) to forward declare the enum (NS_ENUM/NS_OPTION) in objective-c is to use the following:

// Forward declaration for XYZCharacterType in other header say XYZCharacter.h
typedef NS_ENUM(NSUInteger, XYZCharacterType);


// Enum declaration header: "XYZEnumType.h"
#ifndef XYZCharacterType_h
#define XYZCharacterType_h

typedef NS_ENUM(NSUInteger, XYZEnumType) {
    XYZCharacterTypeNotSet,
    XYZCharacterTypeAgent,
    XYZCharacterTypeKiller,
};

#endif /* XYZCharacterType_h */`

Similar question Forward-declare enum in Objective-C

score 0 · Answer 3 · answered May 06 '11 at 04:54

Forward declaration of classes is necessary to enable two classes to refer to each other. It's not uncommon to have two classes that are defined in terms of each other:

@class ClassB;

@interface ClassA : NSObject
{
    ClassB *objectB;
}
@end

@interface ClassB : NSObject
{
    ClassA *objectA;
}
@end

There's no way to make that compile without the forward declaration.

The same is not true of enumerations. enum just creates a set of named values... you can't include one enumeration in the definition of another. Therefore, there's never a need to forward declare an enumeration.

score -1 · Answer 4 · answered May 06 '11 at 03:52

I think what you want is a class that has PasscodeInputMode as a property of it. That way you can be passing around an instantiated object of that class, and can set/get that property, and do other object-like-things with it (assume that's why you'd want to find a "@class equivalent"

@class for typedef enum?

4 Answers4