Can you explain what is meant by associative values in programming?

In programming, especially in iOS development with Objective-C or Swift, associative values refer to a mechanism that allows dynamically adding properties to objects at runtime without modifying their original class.

This is implemented using associated objects in the Objective-C runtime. For example, you can "attach" an additional value to an instance of a class using a key and a pointer to the value. This is useful when you need to extend the functionality of existing classes without creating subclasses.

Example in Objective-C:

#import <objc/runtime.h>

static char kAssociatedObjectKey;

@implementation UIView (CustomProperty)

- (void)setCustomProperty:(NSString *)value {
    objc_setAssociatedObject(self, &kAssociatedObjectKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)customProperty {
    return objc_getAssociatedObject(self, &kAssociatedObjectKey);
}

@end

Here, a new property customProperty is dynamically added to the UIView object without changing the UIView class.