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From: David Abrahams (dave_at_[hidden])
Date: 2004-04-14 09:04:51


I'm just wondering if the deafening silence indicates a lack of
interest or whether something else is going on?
Feedback would be appreciated.


David Abrahams <dave_at_[hidden]> writes:

> I have to stop playing with this stuff and get back to work now, but
> over the weekend I started a library that allows a "reasonably
> convenient, useful amount" of move semantics. Many compilers
> implement enough (N)RVO that implicit moving from rvalues is
> unneccessary, and those seem to coincide roughly with the compilers
> where we have to internally shut off some capability because of the
> compiler's interpretation of 8.5.3/5 (**). So it seems you can pretty
> much eliminate all needless copies.
> Here's what you can do with the current state of the move library,
> which supplies macros (eeeeew!) to avoid code duplication:
> struct X
> : boost::movable<X>
> {
> X, (rhs)(: initializers...),
> {
> // copy ctor body
> })
> X, (rhs),
> {
> // copy assign body
> })
> X(move_from<X> rhs)
> {
> // move ctor logic
> }
> X& operator=(move_from<X> rhs)
> {
> // move assign logic
> }
> };
> boost::movable<X> just encapsulates the conversion to move_from<X> and
> makes the copy ctor/assignment private, so you can always replace it
> with a written-out conversion to move_from<X> if you don't like the
> "MI non-EBO" (or other) impact of library-mandated inheritance.
> This work owes inspiration to Rani Sharoni's "improved auto_ptr"
> ( and of course one must acknowledge Andrei
> Alexandrescu for being crazy enough to even try doing this in a
> library in the first place (Mojo). Eric Friedman had an earlier
> boost/move.hpp in the sandbox based on Mojo (which I replaced with his
> permission), and I adapted his tests, in addition to my own, to work
> with the new code.
> It might make sense to use this library to optimize selected Boost
> components; shared_ptr, any, and dynamic_bitset come to mind, just off
> the top of my head.
> You can find the code in boost/move.hpp and tests in
> libs/move/test/*.cpp. It "basically works" with all MSVC versions,
> Borland, gcc-2.95, gcc-3.3.1, comeau (strict warnings mode only, until
> I find out how to detect that we're in strict errors mode), and all
> intel-win32 versions. I don't know how to make gcc-3.2 work yet.
> The places where it fails, certain things seem to compile which one
> would prefer to cause an error.
> Enjoy,
> Dave
> (**) see
> --
> Dave Abrahams
> Boost Consulting

Dave Abrahams
Boost Consulting

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