Create an Objective C Class at runtime

main.m

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

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    Class myClass = objc_allocateClassPair([NSObject class], "MyClass", 0);
    IMP methodIMP = imp_implementationWithBlock(^(id self) {
      return @"Hello";
    });
    if (!class_addMethod(myClass, @selector(description), methodIMP, "@@:")) {
      exit(1);
    }
    objc_registerClassPair(myClass);
    id classInstance = [[myClass alloc] init];
    NSLog(@"%@", classInstance);
  }
  return 0;
}