Re: [boost] Re: Object Hierarchies using Interface Types with the BIL

From: christopher diggins (cdiggins_at_[hidden])
Date: 2004-12-31 11:09:14

----- Original Message ----- 
From: "Reece Dunn" <msclrhd_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Friday, December 31, 2004 4:26 AM
Subject: [boost] Re: Object Hierarchies using Interface Types with the BIL

> christopher diggins wrote:
>> On the subject of GUI object hierarchies, I wanted to bring to everyone's 
>> attention the Boost Interfaces Library (BIL) currently being developed by 
>> Jonathan Turkanis which could be an excellent tool for building a 
>> flexible and efficient GUI library. There is a brief introduction to the 
>> library on the Boost wiki ( 
>> http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?Boost.Interfaces )
>>
>> The code for declaring the interfaces would look like this:
>>
>> BOOST_IDL_BEGIN(ILabel)
>>  BOOST_IDL_CONST_FN0(GetText, string)
>>  BOOST_IDL_CONST_FN0(GetAlignment, align_T)
>> BOOST_IDL_END(ILabel)
>
> What I am trying to get working is:
>
> 15: BOOST_IDL_BEGIN(IUIObject)
> 16:    BOOST_IDL_FN4(move, void, g::metric, g::metric, g::metric, 
> g::metric)
> 17:    BOOST_IDL_FN2(move, void, g::metric, g::metric)
> 18:    inline void move( g::point p )
> 19:    {
> 20:       move( p.x, p.y );
> 21:    }
> 22: BOOST_IDL_END(IUIObject)
>
> with the latest CVS of Boost, but with msvc-8.0, I get:

> Any suggestions? Is there a version of the BIL that works with the CVS 
> version (or 1.33) of Boost? And is the above valid, since this is the kind 
> of thing I want?

The obvious problem with your code is that the BIL interface is not intended 
to have any function implementation inside of it. It is in this sense more 
like a Java interface or a pure abstract base class. So if you want a move 
functions, I suggest moving them out in a separate class (which I call an 
extension)

template<typename T>
struct IUIObjectWrapper : public T {
  IUIObjectWrapper() : T() { }
  inline void move(g::point p) {
    T::move(p.x, p.y);
  }
}

typedef IUIObjectWrapper<IUIObject> IUIObjectExtension;

This approach actually corrects what I percieve to be a huge flaw with many 
object libraries, which is the coupling of core functionality and derivable 
functionality.

Also note that a new version of the BIL library is due out in a few days.

Christopher Diggins
http://www.cdiggins.com
http://www.heron-language.com