[boost] Re: Closure functions

From: Edward Diener (eddielee_at_[hidden])
Date: 2005-04-15 09:55:37

Tobias Schwinger wrote:
> Hi Community,
> 
> 
> The Function Types library has just been updated to include an 
> implementation of closure functions as an example:
> 
>    [ example (hpp): http://tinyurl.com/9ncso ]
>    [ exmaple (cpp): http://tinyurl.com/9opx6 ]
> 
> You need to have the Function Types library installed if you want to 
> successfully compile it:
> 
>    [ archive (zip): http://tinyurl.com/4oe7q ]
>    [ documentation: http://tinyurl.com/4fw9n ]
> 
> 
> A closure function (in object orientated context) is a member function
> bound to an object.
> 
> Closure functions are well-suited to achieve orthogonal design because 
> they capture member functions independent of their name and class an 
> thus allow to operate on a per-function basis instead of requiring 
> inheritance to e.g. implement classic design patterns such as "Observer".
> 
> In contrast to Boost.Bind (and other Boost argument binding facilities) 
>   closures are intended to be stored and allow the captured target 
> function to dynamically change at runtime.

Boost.Function stores the results of Boost.Bind, and already serves as a 
"closure function".

> 
> 
> Out of curiosity I was wondering if there is a closure function 
> implementation in Boost already (or components that make their 
> implementation trivial - IIRC I have seen something labeled 'closure' in 
> the vault, but I can't find it anymore), whether there is any interest 
> in brushing it up to give it a right to exist somewhere outside an 
> 'example' folder and what requirements you would like it to meet in this 
> case.

See above.

> 
> 
> I know there are "closures" in Boost.Phoenix, but these are about 
> capturing fields, which is not quite the same and why I used the term 
> "closure function" instead of "closure" here.
> 
> What I describe here is close to the BCC compiler extension '__closure', 
>   which is used by C++Builder IDE to easily map GUI (and other) events 
> to member functions.

I am well aware of the BCC __closure having programmed with C++ Builder 
for many years. I think that Boost.Function/Boost.Bind adequately 
emulates it in standard C++, while providing richer functionality with a 
slightly more complicated syntax.