support two way data binding

[Raynos]

• observ-struct
• observ-varhash
• observ-array

cc @nrw

[Raynos]

I'm not going to fix observ-array tonight.

There's a bunch of complexity in this problem domain. observ-struct was hard enough.

[kuraga]

@Raynos can you please describe the problem? thanks

[tracker1]

@Raynos this may provide some insight... not sure if it's too slow though... but thought it might help...

https://github.com/benjamine/jsondiffpatch

[Raynos]

I think we fixed observ-array, cannot remember.

[Raynos]

See this issue ( Raynos/observ-array#9 ). cc @kuraga

I never verified whether all the edgecases were handled.

Also see nrw/observ-varhash#1

[kuraga]

Hm... It's difficult to understand, when notes about issues are posted in different components' repositories 😄

[Raynos]

@kuraga distributed conversations :) hard to find them.

It's also not fully documented what two way data binding means. it basically means that if you mutate either the parent or child in both the parent & child get updated.

var parentArr = hg.array();
var childArr = hg.array();

parentArr.push(childArr);

childArr.push(4);
parentArr.get(0).get(0) === 4;

parentArr.set([
  [5]
])
childArr.get(0) === 4;
parentArr.get(0).get(0) === 5;

I'm not really sure what I want the semantics to be in all the edge cases tbh... Whatever makes time travel work.

The whole point is to be able to serialize the entire state of the world at any time and bring it back at any other time. which means appState.set(bigComplexObject) should propogate the changes down correctly to all the places.

[kuraga]

An ObservVarhash is a version of observ-struct that allows adding and removing keys. Mutation of an observable element in the hash will cause the ObservVarhash to emit a new changed plain javascript object.

@nrw does it mean than we can use observ-varhash as a replacement of observ-struct in mercury?

[nrw]

@kuraga observ-varhash does everything that observ-struct does, so we could use it as a replacement. I always use struct when i know my keys are static and i use varhash when i know they'll change. are you just looking to reduce dependencies?

[kuraga]

I'm looking everything to understand every line of mercury 😄

[nrw]

i see. :)

If you look at the source, varhash is just struct with a bunch of bookkeeping for adding and removing keys. You could just use varhash all the time, if you like.

[Raynos]

I use struct to communicate "these are fixed keys"

I use varhash to communicate "there are N keys"

There is a different, a struct can be like struct({ n: string, m: number })
A varhash should be homogenous so each key should have the same shape varhash({ a: componentT, b: componentT })

[cellvia]

I'm not really sure what I want the semantics to be in all the edge cases tbh... Whatever makes time travel work.

@Raynos or anyone, could you explain this a little further (what would/wouldnt make time travel work, what are examples of edge cases in the context of Raynos sample above)? im a bit new to all this, but may contribute as im noticing observ-array being a bottleneck in my project

[Raynos]

@cellvia last time I looked at this I observed that using varhash instead of array is better in general.

Most of the time you have an array of objects; you can just create a varhash indexed by id or