What does the question mark and the colon (?: ternary operator) mean in objective-c?

objective-c c syntax operators conditional-operator

This is the C ternary operator (Objective-C is a superset of C):

label.frame = (inPseudoEditMode) ? kLabelIndentedRect : kLabelRect;

is semantically equivalent to

if(inPseudoEditMode) { label.frame = kLabelIndentedRect;} else { label.frame = kLabelRect;}

The ternary with no first element (e.g. variable ?: anotherVariable) means the same as (valOrVar != 0) ? valOrVar : anotherValOrVar

objective-c c syntax operators conditional-operator

It's the ternary or conditional operator. It's basic form is:

condition ? valueIfTrue : valueIfFalse

Where the values will only be evaluated if they are chosen.

objective-c c syntax operators conditional-operator

Simply, the logic would be

(condition) ? {code for YES} : {code for NO}

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