Swap class selectors with a block

gistfile1.m

#import <objc/runtime.h>
#import <objc/message.h>

SEL SHNSwapSelectorWithBlock(Class class, SEL selector, BOOL isClassMethod, id block) {
	Method method1 = isClassMethod ? class_getClassMethod(class, selector) : class_getInstanceMethod(class, selector);

	// Generate new selector to inject
	SEL newSelector = NSSelectorFromString([@"_swappedBlock_" stringByAppendingString:NSStringFromSelector(selector)]);
	
	// Inject the block as method in the class
	class_addMethod(object_getClass(class), newSelector, imp_implementationWithBlock(block), method_getTypeEncoding(method1));
	Method method2 = isClassMethod ? class_getClassMethod(class, newSelector) : class_getInstanceMethod(class, newSelector);

	if(method2 != NULL) {
		// Success! Swap the selectors and we're done
		method_exchangeImplementations(method1, method2);
		return newSelector;
	} else {
		// Something broke :(
		return NULL;
	}
}