Re: [boost] [move] new rvalue reference emulation

Subject: Re: [boost] [move] new rvalue reference emulation
From: Jeffrey Lee Hellrung, Jr. (jeffrey.hellrung_at_[hidden])
Date: 2011-04-11 16:24:55

2011/4/11 Ion Gaztañaga <igaztanaga_at_[hidden]>

> El 11/04/2011 3:22, Jeffrey Lee Hellrung, Jr. escribió:
>
>> On Mon, Apr 4, 2011 at 10:36 AM, Jeffrey Lee Hellrung, Jr.<
>> jeffrey.hellrung_at_[hidden]>  wrote:
>> [...snipping original description...]
>>
>
> Sorry for the lack of feedaback! I tried to your example in some compilers
> and checked that MSVC7.1 does not like pointer to function storage in the
> generic rv (it's a msvc bug, but annoying, nevertheless).

It sounds like that could be easily worked around without too much
obfuscation.

> I've been very busy with several interprocess issues and I couldn't take
> time to study this but I promise to dedicate some time soon.

Great, thanks; as long as I know that you've seen the message, I'm happy :)

> I was a bit confused as you use a function object in your example. Can't we
> take rid of that function object and apply it to free functions?

You can, but you would still need a function object to execute the visitor
pattern on the genrv object, since the visitor must be polymorphic (it must
accept many different argument types).  Making the function object *both*
the visitor *and* the "housing" of the overload set is merely a convenience.

> How can we apply this to the constructor of an object?
>

Unfortunately, here the technique can get quite cumbersome.  After thinking
a little about this, I think you'd have to be in one of the following
situations:
- Use no initializer lists, and perform the construction in an "init"
method.  This should be okay for, e.g., pimpl classes.
- All member object(s) and base class(es) that receive the to-be-forwarded
argument can accept a genrv object.
- Use some kind of "typeless opaque storage" for all member object(s) that
receive the to-be-forwarded argument to delay initialization until the
constructor body.  Should be strongly discouraged, but sometimes you gotta
do what you gotta do...

- Jeff