Here are three reminders about copy elision:

1. Copy elision doesn’t happen if your constructor is using a universal reference

If you write a class such as this, there will be no copy elision:

template <typenameT>
class Foo
{
	Foo(T&& other)
	{}
}

This is because functions with universal references are not considered to be copy/move constructors by the compiler.

2. Before C++17, different compilers might act in different ways regarding copy elision.

Copy elision was optional, and implementation-specific for most compilers before C++17. The picture is more varied the further back in time you go, so it’s not reliable.

3. Distinguish between RVO and NRVO.

RVO (return value optimisation) happens when you return a temporary, and is mandatory since C++17:

Foo bar()
{
	return Foo();		//no copying happens for sure
}

NRVO (named return value optimisation) is not mandatory but very often happens:

Foo bar()
{
	Foo f;		
	return f;			//no copying happens some of the time
}