Should the out keyword still be used to annotate output parameters of Objective-C methods?

Question

Created May ’20

Replies 1

Boosts 0

Views 1.2k

Participants 1

Some headers still use the `out` keyword when declaring out paramaters of Objective-C methods, e.g. `- (BOOL)setWLANChannel:(CWChannel *)channel error:(out NSError **)error NS_AVAILABLE_MAC(10_7);`

Is there practical difference when this keyword (qualifier?) is present / abscent for ObjC/ObjC++ (ARC / non-ARC), Swift or AppleScript?

The only relevant reference I have found is in Objective-C Automatic Reference Counting doc for Clang, in the section 4.3.4:

4. If the parameter is not an Objective-C method parameter marked

out

, then

*p

is read, and the result is written into the temporary with primitive semantics.

It's not clear to my why "out" makes such a difference.

Answered by Kentzo in 422102022

Answering my own question: `out` tells the compiler that current value of the retainable object pointer is of no importance to the receiver which allows to elide some retain / release calls. The usecase documented above is actually the only usecase in Apple Clang 11.0.0

Boost

Answer 1

Kentzo OP

May ’20

Accepted Answer

Answering my own question: `out` tells the compiler that current value of the retainable object pointer is of no importance to the receiver which allows to elide some retain / release calls. The usecase documented above is actually the only usecase in Apple Clang 11.0.0

0