Subject: Re: [boost] Pimpl Again?
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2016-06-09 14:59:17
On Thu, Jun 9, 2016 at 5:19 AM, Rainer Deyke <rainerd_at_[hidden]> wrote:
> On 08.06.2016 23:57, Emil Dotchevski wrote:
>
>> On Wed, Jun 8, 2016 at 2:29 PM Rainer Deyke <rainerd_at_[hidden]> wrote:
>>
>> 3. I want a class to have value semantics, but use a copy-on-write
>>> implementation behind the scenes.
>>>
>>
>> Pimpl is not about semantics, it's about reducing physical coupling. It's
>> not about the pointer pointing at the private implementation object
>> (which,
>> being private, is an implementation detail anyway), it's about the private
>> implementation *type* being left incomplete.
>>
>
> Pimpl is a technique where the implementation of a class is moved to a
> separate implementation class (the "impl"), to which the interface class
> maintains a pointer (the "p").
The "p" stands for "private" not for pointer. The defining property of the
pimpl idiom is that the private implementation type is left incomplete in
the interface: the pointer is opaque. For example, if you implement
copy-on-write using a pointer to a type that is defined in the interface,
you're not using pimpl. So, logical design (semantics), including copy
semantics, is orthogonal to pimpl.
Emil