No. In this case, it is the purpose of 'scope ref', not is the implementation details.

What is the language semantics and what is the implementation detail - that varies depending on what is properly supported in the language. D explicitly distinguishes lvalues and rvalues, and also defines that rvalue cannot be taken its address (== reference).

The purpose of 'scope ref' is that the parameter can be received both lvalues and rvalues with one function body. To receive lvalues, scope ref should take the address of them. As a conclusion, to receive rvalues temporary creation is necessary in caller site.

Yes, it mostly represents implementation details, but it is still description of language semantics.

This confusion is almost inevitable. Because the essential purpose of 'scope ref' is already "efficiency".

Furthermore, note that the desired "efficiency" is not "the speed of argument passing".

I recognize that it is "to avoid code bloating of function body". If you need "most efficient argument passing", you should choose it from the argument type. 'scope ref' is not a thing to make the choice automatic.