Re: [boost] auto_vector - vector with auto_ptr semantics

From: Jeremy Siek (jsiek_at_[hidden])
Date: 2002-02-04 18:27:23

Nice description and motivation for move semantics.

On Mon, 4 Feb 2002, Howard Hinnant wrote:
hinnan>
hinnan> What remains to be done is to settle on a uniform syntax for move
hinnan> semantics.  John Maddock has suggested:
hinnan>
hinnan> T b = std::move(a);

Would this mean we'd also have to rely on cooperation from operator=?
Wouldn't it be better to keep things simple with something like this
instead:

std::move(a, b);  // a -> b

hinnan> Perhaps boost::auto_vector could experiment with this.  The big
hinnan> stumbling block I've had to date is allowing move from a temporary T,
hinnan> but disallowing move from a const T, and packaging this up in a
hinnan> relatively reusable package so that giving your class move semantics is
hinnan> no harder than giving it copy semantics.

Well, non-const member functions have the property that you can call them
on temporaries but not on const objects. So you could do this:

a.move_to(b);

Of course, this would require invasive changes to current classes, and
couldn't have the same syntax for builtins.

Or perhaps we just need to file a DR to once again allow temporaries to be
bound to non-const references. On the surface that restriction made a lot
of sense, but deep down it was wrong.

Cheers,
Jeremy

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 Jeremy Siek                          http://php.indiana.edu/~jsiek/
 Ph.D. Student, Indiana Univ. B'ton   email: jsiek_at_[hidden]
 C++ Booster (http://www.boost.org)   office phone: [phone]
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