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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?
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In imperative language terms (notably C and C++), where side effects are important, short-circuit operators introduce a sequence point – they completely evaluate the first argument, including any side effects, before (optionally) processing the second argument.
So when Java finds the value on the left side of an || operator to be true, then Java declares the entire expression to be true. Java's && and || operators use short circuit evaluation.
Short-Circuit Evaluation: Short-circuiting is a programming concept in which the compiler skips the execution or evaluation of some sub-expressions in a logical expression. The compiler stops evaluating the further sub-expressions as soon as the value of the expression is determined.
In C++, both && and || operators use short-circuit evaluation.
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.
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