[QuickSpec] Track the current example within `imp_implementationWithB…

…lock`

This eliminates Objective-C's associated objects usage and overriding `-setInvocation:`.

Sources/QuickObjectiveC/QuickSpec.m

@@ -1,13 +1,10 @@
 #import "QuickSpec.h"
 #import "QuickConfiguration.h"
 #import "World.h"
-#import <objc/runtime.h>
 #import <Quick/Quick-Swift.h>
 
 static QuickSpec *currentSpec = nil;
 
-const void * const QCKExampleKey = &QCKExampleKey;
-
 @interface QuickSpec ()
 @property (nonatomic, strong) Example *example;
 @end
@@ -71,16 +68,6 @@ + (NSArray *)testInvocations {
     return invocations;
 }
 
-/**
- XCTest sets the invocation for the current test case instance using this setter.
- QuickSpec hooks into this event to give the test case a reference to the current example.
- It will need this reference to correctly report its name to XCTest.
- */
-- (void)setInvocation:(NSInvocation *)invocation {
-    self.example = objc_getAssociatedObject(invocation, QCKExampleKey);
-    [super setInvocation:invocation];
-}
-
 #pragma mark - Public Interface
 
 - (void)spec { }
@@ -105,6 +92,7 @@ - (void)spec { }
  */
 + (SEL)addInstanceMethodForExample:(Example *)example classSelectorNames:(NSMutableSet<NSString*> *)selectorNames {
     IMP implementation = imp_implementationWithBlock(^(QuickSpec *self){
+        self.example = example;
         currentSpec = self;
         [example run];
     });
@@ -132,10 +120,6 @@ + (NSInvocation *)invocationForInstanceMethodWithSelector:(SEL)selector
     NSMethodSignature *signature = [self instanceMethodSignatureForSelector:selector];
     NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
     invocation.selector = selector;
-    objc_setAssociatedObject(invocation,
-                             QCKExampleKey,
-                             example,
-                             OBJC_ASSOCIATION_RETAIN_NONATOMIC);
     return invocation;
 }