Mixin class method in Objective-C #objective-c #mixins #runtime #advanced

objective_c_runtime_mixin.m

// MIXINS
+ (void)mixInto:(Class)destCls
{
    NSAssert([[destCls alloc] isKindOfClass:[UIViewController class]], @"%@ is not a UIViewController subclass", destCls);
    
    void (^inject)(Class, SEL, Class) = ^(Class srcCls,
                                          SEL sel,
                                          Class destcls){
        Method newMethod = class_getInstanceMethod(srcCls, sel);
        class_replaceMethod(destCls, sel, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)); // replace is like force-add, where addMethod fails if exists
    };
    
    inject(self, @selector(prevKeyWindow), destCls);
    inject(self, @selector(setPrevKeyWindow:), destCls);
    inject(self, @selector(modalWindow), destCls);
    inject(self, @selector(setModalWindow:), destCls);
}