[swift-evolution] Will Swift ever support optional methods without @objc?

[Karl]

> On 16 Nov 2016, at 03:42, Charles Srstka <cocoadev at charlessoft.com> wrote:
> 
>> On Nov 15, 2016, at 7:27 PM, Karl via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> In Objective-C, asking whether or not an object conforms to a protocol just cascades in to a bunch of calls to “respondsToSelector”, so it’s also very painful.
> 
> This isn’t true; Objective-C stores a list of protocols that a class conforms to, so -respondsToSelector: does not need to be called when checking protocol conformance (also: simply adopting a protocol’s methods will not cause a class to conform to the protocol).
> 
> You can test this yourself:
> 
> #import <Foundation/Foundation.h>
> 
> @protocol P
> 	
> - (void)foo;
> 	
> @end
> 
> @interface C: NSObject<P>
> 
> - (void)foo;
> 
> @end
> 
> @implementation C
> 
> - (void)foo {
> 	NSLog(@"foo");
> }
> 
> - (BOOL)respondsToSelector:(SEL)selector {
> 	NSLog(@"respondsToSelector: called");
> 	
> 	return [super respondsToSelector:selector];
> }
> 
> @end
> 
> int main(int argc, char *argv[]) {
> 	@autoreleasepool {
> 		C *c = [C new];
> 		
> 		NSLog(@"C is P: %@", [c conformsToProtocol:@protocol(P)] ? @"YES" : @"NO");
> 	}
> }
> 
> The output is only:
> 
> C is P: YES
> 
> The log we put in -respondsToSelector: never gets printed.
> 
> Charles
> 

Huh. I’ve been using Objective-C for maybe 15 years and I’ve always avoided “conformsToProtocol” because I didn’t think it gave a strong contract like that. You learn something new every day :)

- Karl
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