Re: [boost] [pimpl] Mini Review

Subject: Re: [boost] [pimpl] Mini Review
From: Vladimir Batov (vb.mail.247_at_[hidden])
Date: 2011-05-28 17:55:34

> Krzysztof Czainski <1czajnik <at> gmail.com> writes:
> 
> I just wanted to add an example...
> I think Pimpl should have the following property:
> 
> a)
> struct X
> {
>   int f();
> private:
>   int a_;
> };
> 
> b)
> struct X : public pimpl<X>::value_semantics
> {
>   int f();
> };
> 
> The user of class X should not be able to tell the difference between a) and
> b).
> 
> X x;
> 
> Now in this case the user can tell the difference. In b) he can do x.null(),
> but in a) he can't. So Pimpl changes the interface. And that's what I want
> to avoid. Pimpl or no Pimpl, the interface of X should stay the same.

1) I firmly believe that the insistence on no difference between a) an b) is
misguided. You are applying a programming pattern/idiom and you reap the
benefits of that applications.

2) That said I do see your desire to deny x.null() to the user. I'd be
interested to know why you are not noticing/satisfied with the obvious solution 

struct X : pimpl<X>::value_semantics { ...}

V.