RE: [boost] Callbacks Again

From: Gary Powell (Gary.Powell_at_[hidden])
Date: 2000-11-16 17:55:07

> 1.  Need to allow traditional functor types as the callback so that 
> function pointers, standard functors, hand coded functors and Lambda 
> Library style functors can all be used with relative ease.
Yes, this style was used in the ScopeGuard, and it works
well with Lambda functors, and std binders.

> 2.  The callback type(s) should be templatized on the return type and 
> argument types, but not on the functor type to simplify useage.
There may be issues with partial declaration of the functor, but in general
it makes using one very easy.

> 3.  Copying a callback should be quick, on par with copying a 
> function pointer.  This is not gauranteed with functors but becomes 
> somewhat important with callbacks that may be stored, copied and 
> passed around frequently in some cases.
If the callback is a "base pointer" to a callback this should be trivial.
The Janitor class that is in ScopeGuard does this using an auto_ptr<>.

> 4.  A callback should itself be a functor.
This falls out of requirement #2.

> 5.  Compiler type coercion should be possible to apply to the functor 
> that the callback wraps for all parameters and the return value.
The lambda library has such tools. (Peter's version does too.) We recently
added the 4 std casts as well.

> 6.  Executing a callback should be nearly as efficient as executing 
> the contained functor.
This is also very compiler dependent. But in general should be a  pointer
deference, and then the function call.

> (I'm chewing on several Boost related things right now, so if there's 
> someone else interested in tackling this I'd prefer it.  If there 
> isn't then I'll have to tackle it, because this is going to be a 
> fundamental requirement for threads.)
> 
If there is any support that LL could provide to make this easier I'm
willing to help out. Jaakko and I are dealing with some of these issues
right now.

-gary-

gary.powell_at_[hidden]