CODEWITHSUNDEEP
objective-cxcode
Sean Danzeiser
Sean Danzeiser

Reputation: 9243

Objective C Ternary operator gives error: implicit conversion to 'void' is disallowed with ARC

I'm finding that the current production version of Xcode is giving me an error when I use the ternary operator like so:

//If address.title is not nil, leave it alone. Else, set it to @"".
address.title   ?: [address setTitle:@""];
address.street  ?: [address setStreet:@""];

When I use a beta preview for Xcode 5.1, i get no such warning. What gives?

Upvotes: 0

Views: 146

Answers (2)

Martin R
Martin R

Reputation: 539695

"Conditionals with Omitted Operands" are a GCC extension (also understood by Clang), and

address.title ? : [address setTitle:@""];

is equivalent to

address.title ? address.title : [address setTitle:@""];

with the only difference that address.title is evaluated only once.

Now the second operand has pointer type (NSString *) and the third operator has void type. In this case the result type of the conditional expression would be void, but ARC does not allow the implicit conversion of NSString * to void. This would compile:

 address.title ? (void)0: [address setTitle:@""];

but, as Merlevede already said, it is much clearer to use an explict if-statement.

If the compiler contained in the beta preview for Xcode 5.1 does not give an error then it could be a bug in the compiler. Of course it could also be another language extension that I do not know of!

Upvotes: 1

Merlevede
Merlevede

Reputation: 8170

Your syntax is wrong

 address.title   ?: [address setTitle:@""];

should be

 address.title =  (address.title)? address.title : @"";
 // or
 [address setTitle:((address.title)? address.title : @"")];

The general syntax is 

 var = (condition) ? value_if_true : value_if_false;  // general syntax

In your case it would be better to do

if (!address.title)
    address.title = @"";

Upvotes: 0

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