CODEWITHSUNDEEP
objective-c
Foredoomed
Foredoomed

Reputation: 2239

Why can NS_ENUM be defined in that way

Am new to Objetive-C and today i encountered NS_ENUM marco which can be used like:

typedef NS_ENUM(Type, MyType) {
 Foo,
 Bar
};

The usage is a little bit weird what why typedof must be used here, so i checked the source code of NS_ENUM:

#if (__cplusplus && __cplusplus >= 201103L &&
        (__has_extension(cxx_strong_enums) ||
         __has_feature(objc_fixed_enum))
    ) ||
    (!__cplusplus && __has_feature(objc_fixed_enum))
    #define NS_ENUM(_type, _name)
            enum _name : _type _name; enum _name : _type
    #if (__cplusplus)
        #define NS_OPTIONS(_type, _name)
                _type _name; enum : _type
    #else
        #define NS_OPTIONS(_type, _name)
                enum _name : _type _name; enum _name : _type
    #endif
#else
    #define NS_ENUM(_type, _name) _type _name; enum
    #define NS_OPTIONS(_type, _name) _type _name; enum
#endif

The way NS_ENUM is being defined makes me more confused, because i don't understand the syntax here, could anyone explain the definition from the syntactic perspective in details? Thanks.

Upvotes: 3

Views: 292

Answers (2)

Merlevede
Merlevede

Reputation: 8170

It's a simple string substitution mechanism. This

#define NS_ENUM(_type, _name)
        enum _name : _type _name; enum _name : _type

means that this

typedef NS_ENUM(int, myEnumType)

will be replaced by this

enum myEnumType : int myEnumType;
enum myEnumType : int

From this source you can see that the enum syntax is:

enum [tag] [: type] {enum-list} [declarator];   // for definition of enumerated type
enum tag declarator;   // for declaration of variable of type tag

Upvotes: 4

zaph
zaph

Reputation: 112857

See: NS_ENUM & NS_OPTIONS for complete information and usage.

From NSHipster: "Introduced in Foundation with iOS 6 / Mac OS X 10.8, the NS_ENUM and NS_OPTIONS macros are the new, preferred way to declare enum types."

Upvotes: 2

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