使いどころ？ なにそれ？

あらゆる実装していない引数なしメソッドでnilを返す。

#import "ClassA.h"

#include <objc/runtime.h>

@implementation ClassA
static NSMethodSignature *sSig = nil;

- (NSMethodSignature *)sig
{
    if(sSig) return sSig;
    
    Method method = class_getInstanceMethod([self class], @selector(returnNil));
    const char *encode = method_getTypeEncoding(method);
    sSig = [[NSMethodSignature signatureWithObjCTypes:encode] retain];
    
    return sSig;
}
- (id)returnNil
{
    return nil;
}
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;
{
    NSString *selName = NSStringFromSelector(aSelector);
    if(![selName hasSuffix:@":"]) {    //  引数なし
        return [self sig];
    }
    
    return nil;
}
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    NSMethodSignature *sig = [anInvocation methodSignature];
    if(sig == [self sig]) {
        [anInvocation setSelector:@selector(returnNil)];
        [anInvocation invokeWithTarget:self];
        return;
    }
    
    [self doesNotRecognizeSelector:selector];
}
@end

使いどころはある！