Move constructor called with copy elision?

In C++17 this is no longer an "Optimization", but part of the "Language Semantics".

Or, more generally, in C++14 a temporary object is first created and then moved to dl. But in C++17, according to the principle of guaranteed copy elision , the object is created directly in dl. So, in the end, neither a copy nor a move is performed.

Resources:

• https://en.cppreference.com/w/cpp/language/copyelision.html
• https://devblogs.microsoft.com/cppblog/guaranteed-copy-elision-does-not-elide-copies

c++17 added "guaranteed elision". With guaranteed elision, prvalues are not materialized until needed. When used to construct an object, they directly construct the object.

In c++14, prvalues are temporary objects, and in certain circumstances the move construction is permitted to be skipped and you can merge to objects into one lifetime.

The difference is here:

struct Data {
  Data() {
    std::cout