Re: Automatially move from $n (was: C++11 move semantics)

[Frank Heckenbach]

Hans Åberg wrote:

> >> One idea might be to wrap the actions in inlines, and use return instead, 
> >> as C++ can recognize r-values in such situations.
> > 
> > I think we discussed this before, but this would only cover the case
> > "$$ = $N" (which is covered by the default action for N = 1 anyway).
> > 
> > More interesting are cases such as:
> > 
> >  $$ = make_unique <foo> ($1, $2, $3);
> 
> The idea would be to write something equivalent to
>   return make_unique<foo>($1, $2, $3);
> and the Bison writes something like
>   $$ = std::move(action_k(...return make_unique<foo>($1, $2, $3);...))

I don't follow you. What is action_k, and how would that cause
moving from $1 etc.?

> Even in view of copy elision, default in C++17 [1], this would be safe, 
> because one cannot move an already moved object by mistake.

Why not?

> As the point is breaking out of the execution path, one might use your 
> suggestion of a special operator in combination with an immediately following 
> break in the action switch statement. So writing say
>   $$$(make_unique<foo>($1, $2, $3));
> translates into
>   $$ = std::move(make_unique<foo>($1, $2, $3));
>   break; 

What if I want to write:

  $$ = make_unique <foo> ($1, $2, $3);
  print ($$);

Regards,
Frank