Blocks in g++ ?

[Per Bothner]

"Thomas Steffen" <for_replies_only@iname.com> writes:

> Per Bothner <bothner@pacbell.net> wrote:
>     Per> (Creating closures is probably not practical unless you have
>     Per> garbage collection.)
> 
> that would explain why i have found only one case of closures in a
> compiler (one of the objective-C compilers, not gcc). could you
> explain why? 

Closures are objects.  (You can simulate objects using closures and
vice versa, fairly painlessly.)  The problems is how to reclaim the
memory used by a closure if you are passing around a reference to
a closure object.  I suppose you might be able to do it with reference
counting.  But that means C++ has to know when it needs to adjust
closure references, which means it needs to know whetheer a pointer
is a reference to a closure or a pointer to a regular function.

I guess with some cleverness one would work out something that
works.  I don't know of anyone having done so, though.  Perhaps
its a cultural thing:  People who want closures also want full
gcc, so it seems pointless to implement closures without gc.

Might make a nice Master's thesis project, though, or an useful
research paper.
--
	--Per Bothner
bothner@pacbell.net     http://home.pacbell.net/bothner/