singleton with "momento"

[FreeSlave]

On Thursday, 9 January 2014 at 21:51:46 UTC, Frustrated wrote:
> Lets suppose I have setup some code to use a singleton object. 
> Now lets suppose I want to duplicate that code(say to run 
> multiple times simultaneously).
>
> The singleton pattern itself prevents multiple copies. One 
> would need multiple instances to be able to run multiple times 
> BUT in the context of each piece of code the object would be a 
> singleton.
>
> It seems one would need a singleton would allow in some cases 
> to not be a singleton. While I'm sure there are some ways 
> around this using a singleton directly I wonder if there is any 
> modified pattern to handle this situation?
>
> Basically if one thought of having a signal universe with an 
> object in it that is a singleton, then decided to end up with 
> multiple universes. In this case there would be copies of the 
> singleton pattern but with regard to each universe they should 
> behave as expected... and each universe is completely separated 
> from all the others).
>
> Anyone know how to easily deal with this?
>
> In my code essentially I have a "universal context"(a 
> singleton) that contains some universal objects(singletons). 
> The context is just a container of all the important data that 
> user code needs quick access too.
>
> I know at some point I'll need to have multiple independent 
> contexts to allow for some advanced processing. Hence I can't 
> have them as singletons but I do want some level of 
> uniqueness(No copies floating around in the universe).
>
> (instead of having to save, change, then restore the context 
> for every context switch)
>
> I'm thinking of something like singleton!(class, universe) 
> where universe is an id but I'm not sure if that is quite right.

The requirement of uniqueness is often synthetic. I don't deeply 
understand your situation, but maybe my suggestion would help. 
Create one object for each context. Each context will contain its 
own "singleton". (or vise versa: create your "singletons" and 
make them to contain context). So you can hold context and 
corresponding singleton together. But in this case you can use 
your singletons only in member functions of corresponding 
instance. Static and global functions still have no "singleton" 
that belongs to them, so you probably will need to pass context 
to them.

Also do you mean "Memento"?