Re: [boost] Pimpl Again?

On 05/31/2016 12:56 AM, Rob Stewart wrote:

On May 30, 2016 1:42:39 AM EDT, Vladimir Batov wrote:

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On 2016-05-30 14:18, Gavin Lambert wrote:

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it would be nice to get something like it into Boost. Excellent. I, too, think that something that simplifies The Pimpl Idiom could be a good addition to Boost.

Thank you, Robert, for chiming in. Much appreciated. Maybe this time we'll be able to get enough momentum and to actually get something tangible out of it.

Adding The Pimpl Idiom to a class means splitting the implements across two class: one public and one private. Even then, the private class is, normally nested in the public class so they are tightly related. With your library, that split is carried further by splitting the code across two distinct namespaces. That is, indeed, a style issue, since the code still does the same work. Nevertheless it seems wrong to write the implementation details of one's own class in the (proposed) boost namespace.

Yes, I hear you. And, yes, from a certain angle that might seem wrong... On the other hand, from a certain angle anything might seem wrong... :-) Is it a serious design flaw? I personally do not think so. More so, I personally see it from a different angle. Namely, I read the code below as "Book is declared as a pimpl; then I define the implementation of that pimpl-Book". Seems sensible and even natural: struct Book : public pimpl<Book>::shared {}; template<> pimpl<Book>::implementation {}; So, when it is simply read (rather than mechanically dissected) it does not seem that wrong at all... to me :-) The "boost::" prefix may or may not be explicitly present... It is up to coder's preferences and style.

I've not given any thought to alternatives, so I can only criticize your solution at present.

Thank you for mentioning it. I'll hijack your prop to re-iterate that I very much hope we all can keep the discussion *constructive* and ultimately moving forward. That IMO means picking the best available solution... and "no solution" is not one of the choices. I am sure we'll never get anything that everyone likes. However, a solution is immensely better than no solution. IMO it's important that we get *something* in... The seed that the library will grow, mature, improve from. We have plenty of libs that went through several incompatible changes... It did not make them worse. It made them better. I am not sure if all those improvements (for everyone's benefits) were possible if those libs did not have the visibility, exposure and scrutiny which come with the Boost tag.