Calling a method on an uninitialized object (null pointer)

One thing you should be clear on is that in Objective-C, you don't call a method on an object, you send a message to an object. The runtime will find the method and call it.

Since the first versions of Objective-C, a message to nil has always been a safe no-op that returns nil. There's a lot of code that depends on this behavior.

From Greg Parker's site:

If running LLVM Compiler 3.0 (Xcode 4.2) or later

Messages to nil with return type | return
Integers up to 64 bits           | 0
Floating-point up to long double | 0.0
Pointers                         | nil
Structs                          | {0}
Any _Complex type                | {0, 0}

A message sent to a nil object is perfectly acceptable in Objective-C, it's treated as a no-op. There is no way to flag it as an error because it's not an error, in fact it can be a very useful feature of the language.

From the docs:

Sending Messages to nil

In Objective-C, it is valid to send a message to nil—it simply has no effect at runtime. There are several patterns in Cocoa that take advantage of this fact. The value returned from a message to nil may also be valid:

• If the method returns an object, then a message sent to nil returns 0 (nil), for example:

  Person *motherInLaw = [[aPerson spouse] mother];

  If aPerson’s spouse is nil, then mother is sent to nil and the method returns nil.

• If the method returns any pointer type, any integer scalar of size less than or equal to sizeof(void*), a float, a double, a long double, or a long long, then a message sent to nil returns 0.

• If the method returns a struct, as defined by the Mac OS X ABI Function Call Guide to be returned in registers, then a message sent to nil returns 0.0 for every field in the data structure. Other struct data types will not be filled with zeros.

• If the method returns anything other than the aforementioned value types the return value of a message sent to nil is undefined.