Affected subclauses: [forwardlist]
Return types of remove
, and unique
changed from void
Improve efficiency and convenience of finding number of removed elements.
Effect on original feature:
Code that depends on the return types might have different semantics in this revision of C++.
Translation units compiled against this version of C++ may be incompatible with
translation units compiled against C++ 2017, either failing to link or having undefined behavior.