C++ covariant return types
Description
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
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return new UnicodeSet(pattern)->freeze();Instead you have to
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UnicodeSet *set = new UnicodeSet(pattern);
set->freeze();
return set;Could we change our clone(), freeze(), and similar functions to return same-as-this types?
