Feature Request: Utility function to get the values of an array (similar $Values for Objects)

[EvHaus]

At the moment, flow provides a useful $Values<> type for getting the type of the keys of an Object. Could we also get a utility that gives us the values of an Array, or extend the $Values<> type to support Arrays instead of only Objects.

The specific use case I'm after is something like this:

const list = ['a', 'b', 'c'];

const myFunc = function (key: $Values<typeof list>) {
   console.log(key);
}

// This should be allowed
myFunc('a');
myFunc('b');
myFunc('c');

// This should throw an error because the given argument isn't one of the elements in my Array
myFunc('d');
myFunc('e');
myFunc(0);

[Mr-Wallet]

This may be a duplicate of #961

[gkz]

type ArrayValues<TArr> = $Call<<T>(Array<T>) => T, TArr>;

https://flow.org/try/#0MYewdgzgLgBAHhAXDAggJzQQwJ4B4DkAFgJb4wA+M+ARtgKb4B8MAvDANpGkA0VtDAXQDcAKBFRsABzqoMOAGqYANgFc6EXABV0aZmwAkAYWVLcWxgAodOcwEpWzTb20ZGoiwCISH5NeyLVdVwJaRAAM3gIRlshGAB6OJgAeQBpEU8wkBAfWSx-ZTUNELpwyOjYhJgAUQAlGqSa3g9M7JgwEFhiMCoSMkoaenx0gEZfOXzAoqkSiIRy+MTa+sa2lQBbajo0GGIIHbBQNclMKGJqJRkAd2IoQhhoNC6AcyA

[jcready]

This also works:

type ArrayValues<TArr> = $ElementType<TArr, number>;

[EvHaus]

@gkz @jcready Unfortunately neither of those work for my original use case

type ArrayValues<TArr> = $Call<<T>(Array<T>) => T, TArr>;
// type ArrayValues<TArr> = $ElementType<TArr, number>;

const list = ['a', 'b', 'c'];

const myFunc = function (key: ArrayValues<typeof list>) {
   console.log(key);
}

myFunc('a');
myFunc('b');
myFunc('c');

myFunc('d'); // This should fail but doesn't
myFunc('e'); // This should fail but doesn't
myFunc(0); // This fails correctly

https://flow.org/try/#0C4TwDgpgBAggTnAhiAaogNgVwgZwDwAq8cAfFALxQAkAwhunoSQBTHJMCUFZBANFEQQkA3ACgA9OKihIsBMjRZchYmUpUAouggBbCADtgBcBBUJ++zDoBGEUmNEBjAPb6cwKOgCW7ilADaAOSIgfyB1qFQgY6BALoOLm4eOiAAYpj6jn4AZhmOwF6uUMwA1hAgAFxySKgY2PgyEM7Znj7AJFwA3qJQvYk4ztoAdOjOAOal5RxiAL6iElIEABY+UDhLzpjoACZQtlD0zgDuENuiKemZzMGB0+dpedcRdxeP0bcOkgIrOGsbW7tgEs4McDvooHYQXA9hBHIhMDhoEDoGMvAA3AwHOBjKwGDw+fSBDyuaDNaRLaAQbR6Qy-LzglLVZD3S6Oa7bD4st4QTlAA

It seems to work on types number vs string but doesn't interpret string enums like Flow does with object keys:

// This works great!
const list = {'a': true, 'b': true, 'c': true};

const myFunc = function (key: $Keys<typeof list>) {
   console.log(key);
}

// This is allowed
myFunc('a');
myFunc('b');
myFunc('c');

// This is not allowed
myFunc('d');
myFunc('e');
myFunc(0);