The --fix option on the command line automatically fixes problems reported by this rule.
Requires use of $ReadOnlyArray instead of just Array or array shorthand notation. $ReadOnlyArray is immutable array collection type and the superclass of Array and tuple types in Flow. Use of $ReadOnlyArray instead of Array can solve some "problems" in typing with Flow (e.g., 1, 2).
General reasons for using immutable data structures:
- They are simpler to construct, test, and use
- They help to avoid temporal coupling
- Their usage is side-effect free (no defensive copies)
- Identity mutability problem is avoided
- They always have failure atomicity
- They are much easier to cache
Note that initialization of a variable with an empty array is considered valid (e.g., const values: Array<string> = [];). This behavior resembles the behavior of Flow's unsealed objects, as it is assumed that empty array is intended to be mutated.