Re: [boost] Pimpl Again?

Subject: Re: [boost] Pimpl Again?
From: Vladimir Batov (Vladimir.Batov_at_[hidden])
Date: 2016-05-31 19:21:22

On 2016-06-01 07:10, Emil Dotchevski wrote:
> ...
> header:
> 
> struct foo { int critical_; };
> shared_ptr<foo> create_foo();
> inline void use_foo_critical( foo * p ) { ++p->critical_; }
> void use_foo_not_so_critical( foo * );
> 
> cpp:
> 
> namespace
> {
>   struct foo_: foo
>   {
>     int not_so_critiral_;
>   };
> }
> 
> shared_ptr<foo> create_foo()
> {
>   return shared_ptr<foo>(new foo_);
> }
> 
> void use_foo_not_so_critical( foo * p )
> {
>   foo_ * q=static_cast<foo_ *>(p);
>   ++q->not_so_critical_;
> }
> ...

Hmm, we probably need to adjust your example (admittedly written in a 
hurry)   -- "foo" needs to be virtual (given we wanted efficiency), 
static_cast kills all C++ advances in type-safety... So, probably it 
should better be

struct foo_;
struct foo { int critical_; shared_ptr<foo_>; };
shared_ptr<foo> create_foo();

Then, when you throw in access restrictions (public/private) as Robert 
mentioned, those free functions need to be declared friends -- a fix due 
to initial "design simplification" -- violation of the association 
between data and behavior.

... And that's where the free-function-based API approach unfortunately 
seems to begin to start faltering as the beauty of simplicity is 
gradually fading away.

Please do not take it as a criticism. I am just thinking aloud to see 
how far your approach can take us (how "scalable" it is :-)) and I hope 
you'll correct me if I veer in the wrong direction.