Feature Request: Singletons and Pool with limits

[pjebs]

1. I created a package called: https://github.com/rocketlaunchr/go-pool. It is a thin wrapper around a sync.Pool but with the ability to limit how many times an item can be taken from the pool. If all items are taken from the pool, it blocks until an item gets put back into the pool
2. I can't figure out how to use this package so that when Invoke, I can set it up so it pulls an item from the Pool and/or blocks when the limit is reached.
3. I also can't work out how to create singletons so Invoke always returns the same object.

[samber]

The default behavior of do is to return a singleton or create it if it does not exist.