What does the Swizzling technique in programming allow to implement?

Swizzling is a technique in programming, especially in Objective-C and Swift, that allows dynamically changing the implementation of methods at runtime.

With swizzling, you can replace the standard behavior of a method with your own, for example, to add logging, modify logic, or fix bugs without changing the original class code.

An example of usage is intercepting the call to the viewDidLoad method in UIViewController to add additional code during the controller's loading.

Example in Objective-C:

+ (void)load {
    Method original = class_getInstanceMethod(self, @selector(viewDidLoad));
    Method swizzled = class_getInstanceMethod(self, @selector(xxx_viewDidLoad));
    method_exchangeImplementations(original, swizzled);
}

- (void)xxx_viewDidLoad {
    [self xxx_viewDidLoad]; // call the original viewDidLoad
    NSLog(@"viewDidLoad called");
}

Thus, swizzling allows changing the behavior of existing methods without inheritance or modifying the original code.