NSArray objectAtIndex: shorthand [duplicate]
This syntax was added in Clang 3.3 : Objective C Literals. Essentially, the compiler converts expressions of the type
objCObj[idx] to the expression
[objCObj objectAtIndexedSubscript:idx]. It also works for dictionaries, and you're free to adopt it for your own objects.
As such, you're perfectly safe using it, assuming you'll be using a modern version of Objective C and suitably updated Objective C compiler (i.e. Clang).