CODEWITHSUNDEEP
flowtype
Tyler Gould
Tyler Gould

Reputation: 82

Refining broad, primitive types into enum types in Flow

I'm writing a function that accepts a string, and if the string value is a member of an enum, I'd like to treat it like the type I've defined for that enum. A simplified example:

const FRUITS = Object.freeze({
  APPLE: 'APPLE',
  BANANA: 'BANANA',
});

type Fruit = $Values<typeof FRUITS>

function fruitChecker(input: string) {
  if (Object.values(FRUITS).includes(input)) {
    (input: Fruit);
  }
}

Example in Flow's web editor

Flow throws an error saying my input in that conditional is not a Fruit. But how can my input not be a Fruit as I've defined it? Is there a right way to perform operations on an enum member after refining the input from a broader, primitive type?

Upvotes: 1

Views: 194

Answers (1)

Ville
Ville

Reputation: 494

See: https://github.com/facebook/flow/issues/6904 and https://github.com/facebook/flow/issues/2221

So .includes can't be used for refinement, and Object.values returns mixed. This means that the scenario you are trying is not currently possible.

Upvotes: 1

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