Re: [boost] Pimpl Again?

Subject: Re: [boost] Pimpl Again?
From: Vladimir Batov (Vladimir.Batov_at_[hidden])
Date: 2016-05-30 01:42:39

On 2016-05-30 14:18, Gavin Lambert wrote:
> On 30/05/2016 15:16, Vladimir Batov wrote:
>> So, in your view, should we try and have pimpl in Boost? I think we
>> should as it'd be useful IMO...
> 
> As I said at the start, yes, I think this has potential usefulness and
> it would be nice to get something like it into Boost.

Excellent.

> ...
> As it's the template specialisation which causes most of my concern,
> my main query is whether it's really necessary or if it could be
> structured differently to avoid this instead.
> 
> ...  Taking the Book example from the docs...
> ... we get something like this:
> 
> namespace library
> {
>     namespace detail
>     {
>         ...
>     }
> }
> 
> namespace boost
> {
>     template<> struct pimpl<library::Book>::implementation
>     {
>         implementation(string const& the_title,
>                        string const& the_author)
>             : title(the_title), author(the_author), price(0)
>         {}
>         ...
>         bool check_isbn_10_digit() { ... }
>         ...
>         string  title;
>         string author;
>         int     price;
>     };
> }
> 
> namespace library
> {
>     Book::Book(string const& title, string const& author)
>         : pimpl_type(title, author)
>     {}
> 
>     string const&
>     Book::author() const
>     {
>         return (*this)->author;
>     }
>     ...
> }
> ...

Yes, I understand. That's why I said before and still insist now that 
that's style... because I personally do not like

namespace library
{
     Book::Book(string const& title, string const& author)
         : pimpl_type(title, author)
     {}
}

as you move your code to the right and IMO just waste the space (you 
fill it with blanks instead of the code). So, I write

template<> struct boost::pimpl<library::Book>::implementation
{
     ....
}

library::Book::Book(string const& title, string const& author)
: pimpl_type(title, author)
{
      ...
}

Then, you might say you do not like fully qualified 
library::Book::Book(), etc... which in my view is, well, style... for me 
the "like" and "do not like" are usually the style triggers.