Flow types on objects

Question

I've been looking at adding Flow to my javascript project.

In several cases, I do something like this, I have an object.

const myObject = {
    x: 12,
    y: "Hello World"
}

And I have a general function that does some mapping on the object, keeping the keys but replacing the values.

function enfunctionate(someObject) {
   return _.mapValues(myObject, (value) => () => value)
}

I'd like the function to return the type {x: () => number, y: () => string} Is there a way to make this happen?

Of course, I could type it more generically as {[key: string]: any} but I'd lose a lot of the static typing I'd like to gain by using flow.

If I could replace my few cases that do this with code generation or macros that could work, but I don't see a good way to do that with flow.

Is there a way to solve this problem?

Answer 1

This is the best you can get at the moment, while it's safer than {[key: string]: any} there's still an any involved

function enfunctionate<O: Object>(someObject: O): { [key: $Keys<O>]: (...rest: Array<void>) => any } {
   return _.mapValues(someObject, (value) => () => value)
}

const obj = enfunctionate(myObject)

obj.x() // ok
obj.unknown() // error

EDIT: starting from v.33 you can use $ObjMap

function enfunctionate<O>(o: O): $ObjMap<O, <V>(v : V) => () => V> {
  return _.mapValues(o, (value) => () => value)
}