// ***** objc
@interface ChildInObjc : ParentInObjc
- (nullable NSString *)text;
@end

@implementation ChildInObjc
- (nullable NSString *)text { return [super text]; }
@end
// *****

// ***** swift
#if swift(>=3.0)
    let parent = ParentInObjc()
    // func text() -> String!
    let parentText = parent.text()   // String?  😇
    let child = ChildInObjc().text() // String?
#else
    let parent = ParentInObjc()
    // func text() -> String!
    let parentText = parent.text()   // String!  😣
    let child = ChildInObjc().text() // String?  😇
#endif
// *****