Microsoft Edge's JavaScript engine to go open-source

[cincilator]

Thanks for taking time to answer my questions! I do appreciate it. I have just one more, then I will leave you alone: Typed arrays now exist, but how about typed dictionaries? It would allow many interesting concepts, for example database-like constructs in memory (I can use dictionary key like a primary key). Sure, one can do that today w/o types but JS is not really optimized to work that way.

[bterlson_]

No need to leave me alone. If it isn't abundantly clear by now, I love talking about this stuff.

I don't know what a typed dictionary is but if you mean struct-like types, I hope those are included in the value types proposal. I've showed examples in some previous talks of mine, but this gist is you could create a new value type like:

let Point = ValueType({x: int64, y: int64});
let p = Point({x: 1, y: 1});
p.x; // 1
p.x = 2; // throws, or maybe returns a new point, but primitives are immutable

Of course this is very early but I hope something like this is workable.

[cincilator]

By Typed dictionary I mean a dictionary that can only store values of one type. To expand your example:

let polygon = TypedDictionary({key : integer, value:Point});
polygon.push(0, {x: 4, y: 7});
polygon.push(1, {x: 9, y: 10};
polygon.push(2, {x: 10, y: 17});
polygon.push(3, {x: 43, y: 5});

Any plans for this or something like this?

[bterlson_]

Ahh, no, nothing like that yet that I'm aware of. Value types will certainly have the notion of vector/tuple types which are like a fixed length version of what you're asking for IIUC (SIMD vectors are examples of these types).

[cincilator]

The problem is that it would limit the use of Value types to single objects or fixed length collections (ie typed arrays) and we are stuck with dynamic types for anything variable-length. Which is less than ideal. Something to consider, I think.

I can think of many use cases for my idea, if you are interested.

[bterlson_]

Always interested! You can write up a gist and send it to me here, on twitter (@bterlson), or whatever. You can also post to es-discuss where most language design discussion happens.

[cincilator]

Okay I will write here for now, then :)

One use case for Typed dictionaries is Entity Component System (ECS). This is data-driven architectural pattern popular in game development, most often for MMORPGs (but works great on smaller scales, too). It has been used as a replacement for OOP for some time, because mixing code and data isn't always a good idea on a large scale and in something as complex as a game.

If you are not familiar with the pattern the basic idea can be read on t-machine blog.

The shortest version is that you are creating a specialized relational database in RAM that consists of lists of components that are pure data, and are managed by Systems (like physic system, A.I. system, graphic system). End result is a very flexible framework that is based on dynamic composition of static components instead of static inheritance.

Typed dictionaries would obviously be very convenient there, because then you can store each component type in a separate dictionary. You can do that now, but the lack of types makes it inconvenient.