Re: [Boost-users] [Signals] Relationships to other libraries and terms

From: Ames Andreas (Andreas.Ames_at_[hidden])
Date: 2006-08-22 06:42:47

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Scott Meyers
> Sent: Tuesday, August 22, 2006 12:07 AM
> Subject: [Boost-users] [Signals] Relationships to other 
> libraries and terms
> 
> We start with "callable entities" -- things that can be called, e.g.,
> function pointers, function objects, bound member functions, 
> etc.  As I
> understand it:
> 
>    - A callback (function or object) is a callable entity
>    - A slot in Boost.Signals is a callable entity
>    - boost::bind and boost::lambda create callable entities.
>    - A boost::function object stores a callable entity.
> 
> We also have collections of callable entities:
> 
>    - A .NET delegate is a collection of 0 or more callable 
> entities with a
>      given signature.
>    - A signal in Boost.Signals is a collection of 0 or more callable
>      entities with signatures compatible with a given signature.
> 
> Objects of these collection types are also callable entities:
> 
>    - When a Boost.Signals signal or a .NET delegate is 
> called, it invokes
>      the callable entities it contains.
> 
> Is that correct?
> 
> Also, does anybody know where the name "slot" comes from in 
> this context?
> I've found this term to be a stumbling block for trying to 
> understand this
> stuff.

I think the callability of signals is just a detail.  Libsigc++ seems to prefer signal.emit() (although they also have operator()).

A slot corresponds to the Observer (in the corresponding GoF pattern), i.e the receipient of a signal (which comes closest to the subject in the GoF pattern).

Regarding the terminology:  IIRC, it was introduced by a signal/slot lib in C, unfortunately I can't find the links, sorry (I'd also be interested in them, if anyone can find them).  There are quite some implementations in C++:  Qt, libsigc++, boost and others.  On the libsigc++ mailing list was a discussion about the terminology, you can find it in the thread starting with http://mail.gnome.org/archives/libsigc-list/2005-July/msg00014.html.

cheers,

aa

-- 
Andreas Ames | Programmer | Comergo GmbH |
Voice:  [phone] | ames AT avaya DOT com