Question

Is it better to create a local object for later use like

NSDictionary *dic = [NSDictionary Dictionary];

or

NSDictionary * dic = nil;

Is it preference thing or is one better then the other?

Answer 1

it’s not like ‘the one is better’, it’s like ‘the other is bad’.

If you’re going to assign a new object to it later, initialize it to nil, else (you leak memory by losing the reference to the first object created by error.) – EDIT: no, you’re not leaking memory (either because of the autorelease or the automatic reference counting, but anyway, that’s an extra unneeded method call.) That is bad.

If it’s a mutable collection, create it before you use it, else it will continue being nil and ignoring essentially all messages sent to it, which is also bad.

Conclusion: it’s not a matter of preference – you must think logically and choose whichever is suited for the specific purpose you are using it for.