How is comparing operator '==' for NSObject [duplicate]

Question

This question already has answers here:

Should you use 'isEqual' or '=='? (2 answers)

Closed 9 years ago.

How is comparing operator '==' for NSObject? Method -isEqual: works fine for me, but when I'm using -isEqual I need to check if objects exists. With '==' I don't need to check this but where I can find documentation for it?

Answer 1

From Apple documentation:

Returns a Boolean value that indicates whether the receiver and a given object are equal. (required) This method defines what it means for instances to be equal. For example, a container object might define two containers as equal if their corresponding objects all respond YES to an isEqual: request. See the NSData, NSDictionary, NSArray, and NSString class specifications for examples of the use of this method. If two objects are equal, they must have the same hash value. This last point is particularly important if you define isEqual: in a subclass and intend to put instances of that subclass into a collection. Make sure you also define hash in your subclass.

if you do like this

if([obj1 isEqual:obj2])

and obj1, or obj2 is nil then you will get NO. (if this is what you meant by your question)
- Now

if(obj1 == obj2)

This is a pointer comparison. Pointers

Answer 2

The == operator tests whether the two expressions are the same pointer to the same object. Cocoa calls this relation “identical”

To test whether two objects are equal, you would send one of them an isEqual: