Re: move constructors likely a requirement

[John W. Eaton]

On 9/5/19 12:35 PM, Carlo De Falco wrote:

> I still see the following 14 instances of -Wreturn-std-move instead :
>
> 14 matches for "-Wreturn-std-move" in buffer: untitled
>      412:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      425:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      438:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      451:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      467:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      483:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      499:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      515:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      531:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      547:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      563:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      579:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      595:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>      611:octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' 
> will be copied despite being returned by name [-Wreturn-std-move]
>
>
> the full warning messages look like this :
>
> octave/libinterp/corefcn/tril.cc:122:14: warning: local variable 'r' will be 
> copied despite being returned by name [-Wreturn-std-move]
>        return r;
>               ^
> octave/libinterp/corefcn/tril.cc:173:41: note: in instantiation of function template 
> specialization 'do_triu<double>' requested here
>    return lower ? do_tril (a, k, pack) : do_triu (a, k, pack);
>                                          ^
> octave/libinterp/corefcn/tril.cc:221:18: note: in instantiation of function template 
> specialization 'do_trilu<double>' requested here
>          retval = do_trilu (arg.array_value (), k, lower, pack);
>                   ^
> octave/libinterp/corefcn/tril.cc:122:14: note: call 'std::move' explicitly to 
> avoid copying
>        return r;
>               ^
>               std::move(r)

I'm surprised those are the only warnings, and that there is a warning 
on line 122 but not also for line 107 in the same function.

jwe