Is prefs a predefined keyword when nesting method calls in Objective-C ?

Question

Hi,

I am working through a book on Cocoa and Objective-C. In the example for nested method calls:

[NSString stringWithFormat:[prefs format]];

I am assuming that prefs is the return type for the nested method call to format...is this correct ?

Thanks,

Scott

Answer 1

Nope, in that case prefs will be an instance of an object. The return type will be an NSString *, since that's what stringWithFormat: takes. If it's part of a wider example then look for a declaration of the 'prefs' object. If it's just a throwaway line then you'll have to trust me for now. Rest assured: [object message] always sends that message to that object. The return type is defined by the message declaration and is assumed to be 'id' if the declaration can't be found.

It's not a particularly safe bit of code, by the way. If the result of [prefs format] contains any formatting characters then NSString will attempt to access things on the call stack that aren't there.

Answer 2

No, the return type is only shown in the function declaration. Prefs is the name of the object whose method is being called (or the receiver, in Obj-C speak). In a Java-type syntax, the line would look like

NSString.stringWithFormat(prefs.format());