Does Objective-C support class variables?

Question

I know it supports automatic variables, but what about class variables?

Answer 1

The language does not support class variables. You implement class-specific state with global static variables in the compilation units of the implementation.

In the header (.h file):

@interface MyClass : NSObject
+(int)val;
@end

In the implementation (.m file):

static int val = 123;

@implementation MyClass
+(int)val {return val;}
@end

Usage:

if ([MyClass val] > 100) ...

Answer 2

ObjC class variables are plain old static variables.

Foo.m:

static int foo = 0;

Alternatively, you can use a C++ anonymous namespace if you use ObjC++:

Foo.mm:

namespace {
    int foo = 0;
}

But there is another pattern if you want to benefit from the advantages of properties:

Foo.h:

@interface FooShared

@property ( atomic, readwrite, strong ) Foo* foo;

@end

@interface Foo

+ (FooShared*) shared;

@end

Foo.m:

@implementation FooShared
@end

static fooShared* = nil;

@implementation Foo

+ (FooShared*) shared
{
    if ( fooShared == nil ) fooShared = [FooShared new];

    return fooShared;
}

@end

somewhere.m:

Foo* foo …;
foo.shared.foo = …;

It may look a bit overkill, but it's a interesting solution. You use the same constructs and language features for both instance properties and "class" properties. Atomicity on demand, accessors when needed, debugging, breakpoints... Inheritance even.

Creative minds can find other ways to do all this I suppose. :) But you're pretty much covered with these options.