[Dlang-study] [lifetime] destructor, difference between C++ and D and rationale

[deadal nix]

Thanks, that's clearer.

2015-10-29 5:39 GMT-07:00 Andrei Alexandrescu <andrei at erdani.com>:

> On 10/28/2015 08:29 PM, deadal nix wrote:
>
>> I think it is very relevent here as destructor is a very common tool to
>> free resources, as well as one of the most complex to deal with, mostly
>> because of move semantic. I already had in mind to launch that subject
>> before this whole thing started.
>>
>> Why were things changed that way ?
>>
>
> On second thought this might inform the best way to go about assigning
> responsibility for inc/decref across the caller and callee.
>
> Regarding object copying: we noticed that in C++ it's difficult to define
> efficient move semantics and forwarding. This is because in a call line
>
> fun(string("hello"));
>
> even if fun "consumes" the string by either returning it or forwarding it
> to another function, the caller of fun must still destroy the rvalue
> created. In C++1x, if move semantics are at work, there's still a need for
> the callee to leave the moved-from string in a well-defined state so the
> destructor doesn't crash. All of that work is unneeded and is required for
> the sake of that destructor call.
>
> In D a key element is that objects are relocatable, i.e. they can be moved
> across memory by using memcpy(). That makes it a more efficient protocol
> possible:
>
> 1. Caller calls the constructor
> 2. Object is bibblitted around
> 3. Object gets destroyed
>
> So in D, perfect forwarding comes for "free" and we don't need a large
> feature such as C++'s rvalue references.
>
> The disadvantage is you can't have value objects with internal pointers.
> (You can still have reference objects with internal pointers.)
>
>
>
> Andrei
> _______________________________________________
> Dlang-study mailing list
> Dlang-study at puremagic.com
> http://lists.puremagic.com/cgi-bin/mailman/listinfo/dlang-study
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.puremagic.com/pipermail/dlang-study/attachments/20151029/369d86b5/attachment.html>