> On Nov 15, 2016, at 7:27 PM, Karl via swift-evolution
> <swift-evolution@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
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