Question

I tried something along the lines of:

if(myString != nil && myString.length) { ... }

And got:

-[NSNull length]: unrecognized selector sent to instance

Does Objective-C not short-circuit after the first condition fails?

Answer 1

Objective-C does support short-circuit evaluation, just like C.

It seems that in your example myString is NSNull and not nil, therefore myString != nil is true.

NSNull is a singleton and is used to represent nil where only objects are allowed, for example in an NSArray.

Btw, normally, people write if (!myString && myString.length == 0). Comparing to nil is quite ugly. Also, I’d compare the length to 0. That seems to be more clear.