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

From: Hans Åberg
Subject: Re: Automatially move from $n (was: C++11 move semantics)
Date: Sat, 15 Sep 2018 21:19:08 +0200

> On 15 Sep 2018, at 20:19, Frank Heckenbach <address@hidden> wrote:
> 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);…))

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.

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));

1. https://en.cppreference.com/w/cpp/language/copy_elision

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