PapaDiHatti questions

• std::map insert thread safe in c++11?
• why const_cast is not allowed for unique_ptr?
• Difference between equivalent and equal for c++20 three way comparison operator?
• Why type qualifiers ignored on function return type only in case of primitives?
• How remove_reference disable template argument deductions?
• Why is this constructor not giving an incomplete type error?

PapaDiHatti answers