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Checking whether an object conforms to two separate protocols in Objective-C

Asked 2011-01-10T11:44:47.053
16

In Objective-C when you declare an instance variable you can check if it conforms to a protocol on assignment at compile time like so:

id <MyProtocol> variable;

Is it possible to check whether an object assigned to the variable conforms to two separate protocols at compile time? As in:

id <MyProtocol, MyOtherProtocol> variable;

I know I can do runtime checking using conformsToProtocol: and respondsToSelector et al, (which I do before actually using the object for added safety), and I could write my own setter method that does the check, but I'd like to know at compile time.

objective-c cocoa cocoa-touch protocols compile-time
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1 Answer

13

I think the best is to use your own code:

id <MyProtocol, MyOtherProtocol> variable;

And before calling a method, check if the variable responds to what you want to call:

if ([variable respondsToSelector:@selector(aMethod:)]) {
    [variable aMethod:nil];
}

Since Objective-C is a dynamic language, just declaring the variable protocol can't assure that it conforms to the protocol. It'll mostly generates warnings when you build.

answered 2011-01-10T14:06:17.463

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