Why NRV Optimization require copy constructor ?

[Dhirendra Singh]

In Stanely B. Lippman book "Inside the C++ object model" it is
mentioned that NRV optimization require explicit definition of copy
constructor. Without copy constructor it is turned off.
I do not understand why it require copy constructor ?
I searched the web but do not find any concrete answer.
Any help on this topic is appreciated.

 

[Bo Persson]

In Stanely B. Lippman book "Inside the C++ object model" it is
mentioned that NRV optimization require explicit definition of copy
constructor. Without copy constructor it is turned off.
I do not understand why it require copy constructor ?
I searched the web but do not find any concrete answer.
Any help on this topic is appreciated.

It doesn't require an explicit copy constructor, but an *accessible*
copy constructor. Making it private would disable returning the value,
even if the copy constructor isn't actually called.


Bo Persson

 

[Abhishek Padmanabh]

In Stanely B. Lippman book "Inside the C++ object model" it is
mentioned that NRV optimization require explicit definition of copy
constructor. Without copy constructor it is turned off.
I do not understand why it require copy constructor ?
I searched the web but do not find any concrete answer.
Any help on this topic is appreciated.

The standards does mention about the copy construction optimization
but it doesn't mention about it be explicitly defined in code
(explicitly here is not related to the keyword 'explicit' or even that
is not required by the standards). So, I don't know what that refers
to, I don't have the book.

 

[Abhishek Padmanabh]

It doesn't require an explicit copy constructor, but an *accessible*
copy constructor. Making it private would disable returning the value,
even if the copy constructor isn't actually called.

Making it private would be pointless. I don't think that would have
been the intent of the author. Because once the copy constructor is
not accessible, you wouldn't even be able to copy-construct or return
by value. So, copy constructor being accessible is kind of like
stating the obvious.