Re: [boost] Should Boost adopt pimpl/d-pointer as much as it can?

Subject: Re: [boost] Should Boost adopt pimpl/d-pointer as much as it can?
From: Vladimir Batov (vbatov_at_[hidden])
Date: 2010-03-20 21:43:54

> From: "Phil Endecott" <spam_from_boost_dev_at_[hidden]>
>> Artyom wrote:
>> 2) Any non-template based class should have opaque/d/pimpl pointer in its
>>    body.
>
> I think that what you have done is the right solution - you, the end user, 
> can wrap things in pimpls where you believe it is beneficial.

I am far from convinced that it is always the right solution to leave that 
descion to the end-user.

> It's fairly easy to convert a non-pimpl interface into a pimpl one, 
> espcially if you need only a subset of it;

I personally spent quite a bit of time looking at the idom and I am under 
strong impression that converting to the pimpl interface *correctly* is not 
*that* straightforward. More so, I am not convinced that giving that 
*option* (or leaving that burden) to the user is such a good idea.

> on the other hand, it's impossible to convert a pimpl'd interface back 
> into a non-pimpled one.

In my experience non-pimpled implementations do make sense. Say, for classes 
of limited complexity (like struct { int a, b; }) where passing by value is 
more efficient. Due to growing complexity of s/w the overhead of pimpl is 
often negligible and, therefore, an intelligent decision can be make by the 
implementer. However, pimpl's benefits are substantial, more importantly for 
*both* the end-user *and* the library developer. Pimpl's important 
properties are the separation of the interface and the implementation *and* 
implementation hiding. The implementation hiding is crucial for 
industrial-grade s/w (which Boost has become) as it frees implementer's 
hands. The user benefits as well, as he/she might not even need to recompile 
to deploy a new shared/dynamic library. I've been deploying Pimpl for a 
while -- eliminated a lot of hassle as far as implementer-user is concerned.

Best,
V.