Persistent datastructure approach to edits about id HOT 4 CLOSED

The basic idea here is that the core object graph is immutable. Edit operations are represented as pure functions that take one object graph and return another. The returned graph shares the subgraphs that haven't changed; for any given edit operation this is likely to be a large proportion of the overall structure.

Another way to think about this is as a fine grained copy-on-write strategy. It's also sometimes called a 'functional core, imperative shell' architecture and is popular for obvious reasons in functional programming. Keeping large sections of your code side-effect free tends to have benefits in testability and ease of reasoning.

Undo/redo in this implementation is trivial-- each undo state has a reference to the object graph at that time and undoing is simply resetting the 'current' reference.

In JS, sharing substructure can be done with shared object references and perhaps prototypal sharing via Object.create. I think es5 even has an Object.freeze that can be used to check our work as far as preserving immutability.

The trade off is that for some operations, updating structure in place is probably easier than copying the parts that change (especially if we have lots of parent references that need to be traversed).

from id.

Okay, so in-between steps from here to there - possibly we should exchange actual object-references in Entity for lists of ids?

And we don't have a real 'parent' element right now - likely the data-storage part of iD.Connection needs to be decoupled from the connection part.

from id.

Okay, so in-between steps from here to there - possibly we should exchange actual object-references in Entity for lists of ids?

An indirection layer that decouples Entity from parents -- I like it.

And we don't have a real 'parent' element right now - likely the data-storage part of iD.Connection needs to be decoupled from the connection part.

Yep. iD.SceneGraph.

from id.

This is now implemented, onto particulars like #64

from id.