Objective-C compiler is leaving out a protocol definition

Question

I'm writing a couple classes that make use of the Objective-C runtime library. This includes retrieving Protocol definitions at runtime based on their name. However, it appears that Protocols that are not explicitly adopted by a class or referenced in code using @protocol(ProtocolName) are excluded from compilation and not available at runtime.

Example:

@protocol MyProtocol <NSObject>

-(void)doSomething;

@end

//Somewhere else in code

Protocol *protocol = NSProtocolFromString(@"MyProtocol"); 
// ^ value of "protocol" will be nil when I run the application!

//However, if I use do the following:

Protocol *whyDoIHaveToDoThis = @protocol(MyProtocol);
Protocol *protocol = NSProtocolFromString(@"MyProtocol"); 
// ^ value of "protocol" will now be a pointer as expected when I run the application!

Does anyone know why this is, and even better, how to force the compiler to include Protocol definitions that are not in use at compile time, but which I will later want available at runtime?

Answer 1

You can force the compiler to include the protocol by making a dummy method that's not called that uses it. I've done this before:

void preserveProtocolFromBeingTrimmed()
{
     (void)@protocol(BrightnessProtocol);
}

I see that Apple uses this in their FxBrightness plug-in from the FxPlug SDK.