Kotlin Function Generics - Upper Bound Not Working I faced some issue regarding usage of Kotlin generics in functions fun doSomething(): T { return String() as T } class Something(intValue: Int) Something(doSomething()) // Doesn't show any compile error Now when it is executed it throws error java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Number Wanted to know why Kotlin compiler is not throwing error for incompatible typecasting