C++ covariant return types

One of the pain points with using ICU C++ API is that some of our subclass functions return pointer-to-base-class, just because 20 years ago some compilers didn't support covariant return types.

(FYI: In Java, covariant return types are supported since Java 5: )

For example, UnicodeSet clone() and freeze() return pointers to the UnicodeFunctor base class, so you can't just write

Instead you have to

Could we change our clone(), freeze(), and similar functions to return same-as-this types?

• https://en.wikipedia.org/wiki/Covariant_return_type

• https://www.lwithers.me.uk/articles/covariant.html

• https://www.learncpp.com/cpp-tutorial/12-2a-the-override-and-final-specifiers-and-covariant-return-types/