Pure functions in D

[downs]

Denis Koroskin wrote:
> On Tue, 23 Sep 2008 02:24:10 +0400, Walter Bright
> <newshound1 at digitalmars.com> wrote:
> 
>> bearophile wrote:
>>>> They can be hot swapped (meaning replaced at runtime), because they
>>>> do not rely on any global initialization or termination state.<
>>>  This sounds true and interesting, but what can it be used/useful for?
>>
>> I've heard mention many times that languages like Erlang allow hot
>> swapping meaning the software can be upgraded without bringing the
>> system to a halt first.
> 
> Yes, Java has some support of hot-swapping, too.
> 
> Imagine you have a MMORPG server. Applying a patch or adding some
> additional content is a daily event. Doing so without disconnecting the
> people (especially if there are thousands of player online) is desirable
> but hardly available in C/C++.

I did that with an IRC bot a while back.

Just build a new executable, halt all your running tasks, dump the system state to a file (*including socket handles*), use the exec system call to replace the process with the new executable, and read the system state back, replacing handles as you go.

No dropped connections.