Introduction
Overview
Weak entry, strong value immutable registry data structure. Think of it as an immutable WeakKeyDictionary.
Motivation
Immutable data structures are great for when you need to implement some kind of “snapshot” of states for easy undo/redo, time-travelling functionality. The library pyrsistent is great for that, but it lacks a map-like structure in which the keys are stored as weak references.
Registtro is an implementation of that structure, which allows for proper garbage collection of the keys/entries, while still allowing to store their states in a centralized, immutable structure.
Example
Simple implementation of an undoable store that keeps track of states for entries.
>>> from registtro import Registry
>>> class Store(object):
... """Keeps track of the history of states for entries."""
... def __init__(self):
... self._done = [Registry()]
... self._undone = []
... def init(self, entry, state):
... self._done.append(self._done[-1].update({entry: state}))
... del self._done[:-1]
... del self._undone[:]
... def get_state(self, entry):
... return self._done[-1].query(entry)
... def set_state(self, entry, state):
... del self._undone[:]
... self._done.append(self._done[-1].update({entry: state}))
... def undo(self):
... assert len(self._done) > 1, "can't undo"
... self._undone.append(self._done.pop())
... def redo(self):
... assert self._undone, "can't redo"
... self._done.append(self._undone.pop())
...
>>> class Entry(object):
... """Reads/sets state in a store."""
... def __init__(self, store, state):
... self._store = store
... store.init(self, state)
... def get_state(self):
... return self._store.get_state(self)
... def set_state(self, state):
... self._store.set_state(self, state)
...
>>> # Initialize entries.
>>> global_store = Store()
>>> entry_a = Entry(global_store, "foo")
>>> entry_b = Entry(global_store, "bar")
>>> (entry_a.get_state(), entry_b.get_state())
('foo', 'bar')
>>> # Modify entries.
>>> entry_a.set_state("FOO")
>>> entry_b.set_state("BAR")
>>> (entry_a.get_state(), entry_b.get_state())
('FOO', 'BAR')
>>> # Undo modifications.
>>> global_store.undo()
>>> (entry_a.get_state(), entry_b.get_state())
('FOO', 'bar')
>>> global_store.undo()
>>> (entry_a.get_state(), entry_b.get_state())
('foo', 'bar')
>>> # Redo modifications.
>>> global_store.redo()
>>> (entry_a.get_state(), entry_b.get_state())
('FOO', 'bar')
>>> global_store.redo()
>>> (entry_a.get_state(), entry_b.get_state())
('FOO', 'BAR')