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

From: Frank Heckenbach
Subject: Re: Automatially move from $n (was: C++11 move semantics)
Date: Sun, 01 Apr 2018 21:47:53 +0200

Hans Åberg wrote:

> >> Maybe Bison might support some additional symbol for move action values, 
> >> like $$k.
> > 
> > I'd thought about this, but it would require changes to Bison itself
> > (for a rather special feature, only for only target language, which
> > can be done in the skeletons), and the user grammar files would also
> > look differently, whereas with my way, they generally look just like
> > they would with shared pointers, or in C, Java, etc., i.e.
> > "$$ = make_foo ($1, $2)".
> > 
> > Also "$$k" would look rather similar to "$$" (probably not strictly
> > a conflict, but maybe confusing).
> Maybe just add to %code:
>   semantic_type&& operator*(semantic_type& x) { return std::move(x); }
> and use *$k, in case this operator is not needed for something else.

If semantic_type doesn't have a "*" operator of its own, this might
work (but look confusing). However, I use the variant (so I'd need
this function for each alternative, which might be possible to do
with templates), but some of my semantic values are (smart)
pointers, so "*" is already used (and even if I could somehow
override it, it would suggest dereferencing rather than moving).

Now, if C++ had a dedicated move operator (which would also be
useful in other code) ... But (ab)using an existing operator seems
confusing to me.


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