Re: [boost] Interest in non-intrusive signal/slot lib?

Subject: Re: [boost] Interest in non-intrusive signal/slot lib?
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2015-05-18 20:04:46

On Mon, May 18, 2015 at 4:22 PM, Gavin Lambert <gavinl_at_[hidden]>
wrote:

> On 19/05/2015 09:36, Edward Diener wrote:
>
>> On 5/18/2015 1:39 PM, Emil Dotchevski wrote:
>>
>>> On Mon, May 18, 2015 at 8:42 AM, Edward Diener <eldiener_at_[hidden]>
>>> wrote:
>>>
>>>> That's not where the confusion existed for me. Gavin Lambert
>>>> explained why
>>>> each signal must be a different type. I realized that a signal is a
>>>> type,
>>>> but not why the same signal could not be used for more than one event (
>>>> button down, button up etc. ).
>>>>
>>>
>>> The signal *is* the event though. So I guess I still don't understand. If
>>> you have two events, "button up" and "button down", then you need two
>>> Synapse signals or else you wouldn't be able to tell them apart.
>>>
>>
>> Your synapse code evidently needs to tell them apart but from the
>> end-user's perspective it isn't necessary, since the only thing he cares
>> about is the parameter types being specified. If he has a signal of:
>>
>> typedef void (*button_signal)(int,int) ;
>>
>> why wouldn't he use it for both a button_up and a button_down event,
>> since it has the correct number and type of parameters for both ?
>>
>
> The key issue is that the list of connected handlers is associated with
> the type (which I did say before, but evidently not clearly enough).
>
> This means that if you use the same type and the same emitter, it's the
> same "signal" and it's not possible to differentiate between them -- you
> can call them "button_down" and "button_up" if you like, but they're just
> aliases for the same thing and using either of them will result in the same
> set of handlers being invoked (which is the union of connections made using
> either name, because again they're just aliases).
>
> If you want separate handler lists (ie. a separate signal) then you have
> to have a separate type, and that requires that the type be unique in some
> way.  The author chose to use the return value for that purpose.
>
> (The implementation stores all connected handlers in a list indexed by
> type, and then at emit time calls only the ones with the correct emitter.)

Gavin, you got it and explained it very well, thank you.

-- 
Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode