Objective-C copy properties

Question

pi1024e OP

Created Apr ’23

Replies 2

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When I have a property like this:

@property (nonatomic, readonly, copy) NSURL *sourceURL; And then I call:

NSURL *url = self.sourceURL;

Assuming that ARC is disabled, to ensure this object does not leak, must I manually release url? If so, how come I don't have to with:

NSURL *url = [NSURL URLWithString:@"http:&#x2F;&#x2F;www.apple.com"];
NSURL *absURL = url.absoluteURL;

Despite the absoluteString property also being readonly and copy:

As per Apple:

@property(nullable, readonly, copy) NSURL *absoluteURL;

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Answer 1

endecotp OP

Apr ’23

I believe "copy" means that it copies the object you supply when you assign to the property. It's not relevant when you read from the property, as in your url = self.sourceURL example.

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Answer 2

DTS Engineer OP

Apple

Apr ’23

If true why would Apple have @property(nullable, readonly, copy) … ?

Because it’s common for APIs to have a private setter. For that to make sense you have to declare the property like that in the header and then, in a private class extension, you declare it readwrite. The copy is saying If this property were settable, it’d use copy semantics.

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