Re: move constructors likely a requirement

[Daniel J Sebald]

On 8/21/19 1:03 AM, Carlo De Falco wrote:
> Hi,
>
> > Il giorno 21 ago 2019, alle ore 00:59, Rik <address@hidden> ha scritto:
> >
> > main ()
> > {
> >    comp_class cobj;
> >
> >    cobj = init ();
> >
> >    ...
> > }
> >
> > comp_class init (void)
> > {
> >    comp_class retval;  // local variable
> >
> >    retval.xxx = yyy;   // initialization
> >    ...
> >
> >    return retval;      // return by value (a comp_class object)
> > }
>
> This may be a naive comment as it is based only on your super-simplified
> and I didn't look at the actual code, but wouldn't it be more simple and 
> efficient
> to change the code pattern above to the following?
>
>
> main ()
> {
>    comp_class cobj;
>
>    init (cobj);
>
>    ...
> }
>
> void init (comp_class& retval)
> {
>    //comp_class retval;  // local variable, no longer needed
>
>    retval.xxx = yyy;   // initialization
>    ...
>
>    //return retval;      // return by value (a comp_class object), no longer 
> needed
> }
>
>
> this is mainly out of curiosity, sorry for the noise if it makes no sense ...
>
> c.

It makes sense; it's one of the alternatives Rik mentioned: "return by 
reference".  That would be my preference, I guess.  I spent decades 
thinking in terms of pointers.  Then references came along and I was 
alright with them--just a little extra sheen.  But as features have been 
added to C++, I always feel a bit more detached and unsure exactly how 
efficient something compiles.

In C and early C++ the return options were limited to basic variables, 
and often there were rules about just what particular registers these 
variable types were stored in... enabling one to be even more efficient 
at things if the values could be kept within the register without having 
to go to memory/stack and back.

Dan