Re: [boost] [pimpl] Some comments

Subject: Re: [boost] [pimpl] Some comments
From: Rob Stewart (robertstewart_at_[hidden])
Date: 2014-06-07 10:08:30

On June 7, 2014 8:05:39 AM EDT, Andrzej Krzemienski <akrzemi1_at_[hidden]> wrote:
>2014-06-06 3:51 GMT+02:00 Vladimir Batov
><Vladimir.Batov_at_[hidden]>:
>> On 06/06/2014 07:21 AM, Andrzej Krzemienski wrote:
>
>I still claim that pimpl::pointer_semantics breaches value semantics
>expectations in an unprecedented way. Both non-const refs and
>shared_ptr,
>and raw pointer and normal value semantic classes have one property in
>common: Their operator== reflects their *salient attributes*. Sorry for
>a
>fancy term. I borrowed it from John Lakos:
>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2479.pdf,
>https://github.com/boostcon/cppnow_presentations_2014/blob/master/files/accu2015.140518.pdf?raw=true

The point of the Pimpl Idiom is to move what would be private data members out of the header. Any semantic thing you would have done, had the members been declared in the header, should be possible after applying the Pimpl Idiom. If value_semantics precludes proper equality comparisons, that's a major problem. If it doesn't preclude them, but changes the default behavior, relative to non-Pimpl classes, it's unfortunate.

___
Rob

(Sent from my portable computation engine)