jeffmo

###v0.18.0

Likely to cause new Flow errors:

• Flow is now stricter (and more consistent) about how null works when used as an initialization value for object properties that are mutated later. So let o = {prop: null}; o.prop = 42; is now an error and requires that null be annotated in the object initializer: let o = {prop: (null: ?number};.
• The return type of RegExp.prototype.match() is now properly annotated to return a nullable. As a result, 0.18 may uncover places where .match() wasn't properly being guarded for a null return value.

New Features:

• We now take advantage of the guarantee that const variables are read-only when doing refinements. This means that refining const variables now has far fewer caveats than refining lets or vars!

jeffmo

/* @flow */

var otherObj = {
  nullableProp: "asdf",
  prop: 42,
};

var a = {nullableProp: null, ...otherObj};

jeffmo

/* @flow */

var otherObj = {
  nullableProp: ("asdf": ?string),
  prop: 42,
};

var a = {nullableProp: null, ...otherObj};

jeffmo

[libs]
types

jeffmo

[libs]
types

jeffmo

// @flow

type Action =
  {type: 'b', prop1: string}
  | {type: 'c', prop2: string};

function onAction(action: Action): void {
  switch (action.type) {
    case 'b':
      // If you comment the following conditional return, Flow stops erroring on

jeffmo

/* @flow */

type Float = number;
type Interpolation<a> = (_:a, _:a, _:Float) => a;

const float: Interpolation<Float> = (from, to, progress) => from + (to - from) * progress;

const a: number = float(42, 42, 42);
const b: string = float('asdf', 'asdf', 42);

jeffmo

/* @flow */

type Float = number;
type Interpolation<a> = (_:a, _:a, _:Float) => a;

const float: Interpolation<Float> = (from, to, progress) => from + (to - from) * progress;

const a: number = float(42, 42, 42);
const b: string = float('asdf', 'asdf', 42);

jeffmo

/* @flow */

var a: {[_:string]:number, b: number} = {
  a: 1,
  b: 2,
}

var b = {c: 'asdf'};

jeffmo

/* @flow */

const run = (task:?Function) => {
  if (task != null)  {
    const safeTask = task;
    const run = () => {
      return safeTask()
    }

    run()