Re: [boost] Signals & slots library prototype

From: Douglas Gregor (gregod_at_[hidden])
Date: 2001-07-04 08:48:58

On Wednesday 04 July 2001 07:36, you wrote:
> From: "Douglas Gregor" <gregod_at_[hidden]>
>
> [...]
>
> > To build the examples & testcases, you will need Boost.Function from CVS
>
> and
>
> > the PREPROCESSOR library currently under review. A modified version of
>
> Peter
>
> > Dimov's bind.hpp is included that implements the interface needed by
>
> signals
>
> > & slots.
>
> Could you please describe your modifications in more detail? bind.hpp is
> still a work in progress. From what I can see, you've added some inline
> functions that can easy go in a separate header; anything else that I've
> missed?
>
> --
> Peter Dimov
> Multi Media Ltd.

That's about it. The changes could go in a separate header but it's a 
dangerous thing to do: if a user includes bind.hpp but not the separate 
header, everything will seem to work but the signals won't know about any 
bound objects; there isn't a very good way to warn the user about this. Since 
visit_bound_objects is such a small bit of code, I'd prefer if it were always 
included in the primary binder library header.

It's the function of visit_bound_objects (and its associated visitor concept) 
that I would like to discuss. Essentially, signals & slots needs the ability 
to access each of the bound objects in a slot (slot = any function object). I 
chose to use a visit_bound_objects free function that takes the function 
object and a visitor, and calls a method in the visitor for each bound 
object. There are lots of open issues, the most important of which are:
        - References: can't tell them apart from by-value at the moment. Perhaps it 
is best to add a "visit_reference" member to the visitor concept.
        - User-defined pointer types: we need to know where a given object is hiding 
inside a user-defined pointer type, and how to access it. This is perhaps a 
separate issue, but is necessary nonetheless. 

        Doug