Defining dynamic but consistent types

The FooByUser object is a simple structure representing the amount of foo performed by each user, setting each property’s key & value to the username & recorded foo respectively.

The collection of keys composing the object may vary between objects representing different periods. For example if new user3 records foo in April then the March and April objects will differ in keys : {user1: 100, user2: 3} vs {user1: 87, user2: 5, user3: 30 }.

From a code documentation perspective I want to define FooByUser as having a set of property keys of known origin & type (if such a word can be used), but which cannot be predetermined for each particular instance.

Could we have a syntax something like the following?

interface FooByUser {
  *<username>: Number
}
def username {
  desc:    "The username of a user",
  source: {type: "database", location: "users.id"} 
}

Where the <> demonstrate that that we are using a def rather than a static key and the * represents that there may be more than one of these keys.

[Mouvedia]

We either should declare and hold to our “different syntax path”, or use existing JS practices and hold to “JS ecosystem syntax path”.

Whenever we can we will provide something that is familiar.

Concerning the declared intents, I am not inclined to edit these: Eric is the one who knows what he envisioned originally. You can do a PR though.

[ericelliott]

It sounds like what you really want is a generic collection, where we don’t care about the names of the keys at all. You could implement such a collection that shares some convenience methods from Arrays using #120:

typeclass Foldable {
  reduce (this: Foldable[a], (accumulator: b, item: a) => b, initial?: a) => b
};

typeclass Semigroup {
  concat (this: Semigroup[a], ...args: [...Semigroup[Any]]) => Semigroup[Any]
};

typeclass Functor {
  map (this: Functor[a], a => b) => Functor[b]
};

typeclass Collection: Foldable & Semigroup & Functor;

interface User {
  name: String,
  number: Number
};

interface UserCollection: Collection[User] & {
  byName (this, name: String) => Number
}

Would that work for your usecase?