Overloading on universal references almost always leads to the universal reference overload being called more frequently than expected.

But don’t apply std::move or std::forward to local objects if they would otherwise be eligible for the return value optimization.

If a function template parameter has type T&& for a deduced type T, or if an object is declared using auto&&, the parameter or object is a universal reference.

std::move performs an unconditional cast to an rvalue, while std::forward casts its argument to an rvalue only if that argument is bound to an rvalue.

For std::unique_ptr pImpl pointers, declare special member functions in the class header, but implement them in the implementation file.