You may have a class that you want to participate in RVO or NRVO, but you also don’t want it to be moved. For example, it may contain a std::mutex, which is not movable. But you nevertheless have to declare a move constructor. What can you do?

The Move Constructor That You Have to Declare, Even Though You Don’t Want Anyone to Actually Call It

by Raymond Chen

From the article:

Blah blah blah C++ return value optimization (RVO), named return value optimization (NRVO), and copy elision.

RVO support was optional in C++11 but became mandatory in C++17. NRVO support remains optional (but recommended).

To allow NRVO in C++17 (or RVO and NRVO in C++11), a move constructor must be available, even though the compiler will not call it if the optimization is employed.

You may have a class that you want to participate in RVO or NRVO, but you also don’t want it to be moved. For example, it may contain a std::mutex, which is not movable. But you nevertheless have to declare a move constructor. What can you do?

Declare the move constructor, but...