Objective-c – “Private methods” or static functions in Objective-C. Which one should I use

cocoaobjective c

When reading Best way to define private methods for a class in Objective-C I end up with a programming style doubt. Which is the better solution (in terms of style) to this problem? To use a category and declare it in the @interface directive in the .m file or go with the static function that receives an object.

Thanks

Best Answer

If you do not have an immediate answer as to which to use, prefer functions.

I use functions most of the time (> 90%).

Methods are useful for polymorphism and the interface.

There are other considerations for each:

Functions will generally be smaller, faster, and the compiler has the ability to inline them. If there is no reason to cause a problem by using a method and you do not need to have any exclusive in-class use, then go with the function.

Methods (or categories, if you prefer) are handy if you don't want accessor overhead or want some other feature which is available in the instance method, such as @synchronized. In my programs, these features are far less likely, and there is usually no need to use methods.

Methods export additional symbols, and generally incur a higher (but small) overhead, as a result, they typically make the binary slightly larger and the executable slightly slower (not usually noticed, unless you use them often).

There is also a risk in using/creating private methods, in that receivers/subclasses may implement/declare the method. It's often an unnecessary risk. I prefer the compiler/linker to sort this out for me, rather than find out that it is hitting an odd case at runtime 2 weeks after shipping (and difficult to locate the problem). Methods may also be useful if you intend on making the interface public sometime soon.

Related Solutions

Objective-c – Best way to define private methods for a class in Objective-C

There isn't, as others have already said, such a thing as a private method in Objective-C. However, starting in Objective-C 2.0 (meaning Mac OS X Leopard, iPhone OS 2.0, and later) you can create a category with an empty name (i.e. @interface MyClass ()) called Class Extension. What's unique about a class extension is that the method implementations must go in the same @implementation MyClass as the public methods. So I structure my classes like this:

In the .h file:

@interface MyClass {
    // My Instance Variables
}

- (void)myPublicMethod;

@end

And in the .m file:

@interface MyClass()

- (void)myPrivateMethod;

@end

@implementation MyClass

- (void)myPublicMethod {
    // Implementation goes here
}

- (void)myPrivateMethod {
    // Implementation goes here
}

@end

I think the greatest advantage of this approach is that it allows you to group your method implementations by functionality, not by the (sometimes arbitrary) public/private distinction.

Ios – What does “@private” mean in Objective-C

It's a visibility modifier—it means that instance variables declared as @private can only be accessed by instances of the same class. Private members cannot be accessed by subclasses or other classes.

For example:

@interface MyClass : NSObject
{
    @private
    int someVar;  // Can only be accessed by instances of MyClass

    @public
    int aPublicVar;  // Can be accessed by any object
}
@end

Also, to clarify, methods are always public in Objective-C. There are ways of "hiding" method declarations, though—see this question for more information.

Best Answer

Related Solutions

Objective-c – Best way to define private methods for a class in Objective-C

Ios – What does “@private” mean in Objective-C

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