typeof loosing type information

[villesau]

See this example

/* @flow */

const shape1 = Object.freeze({
    A: 'value1'
});

const shape2 = Object.freeze({
    A: 'othervalue'
});

//SHOULD FAIL since A differs!
(shape1: typeof shape2);

shape1 matches to typeof shape2 even though the values are totally different. All the objects are frozen. We are not able to type check our static object structures because of this. This is pretty bad and allows the developer to pass any string in without error. The worst thing is that it's not obvious for developer that this happens, flow does not tell anything about missing type information.

[AugustinLF]

If I recall correctly, typeof doesn't turn strings into enum, so here typeof shape1 === { A: string}. That's a know problem that has been raised several times (it's a problem for redux-like constants).

[jcready]

The only workaround right now is to annotate each property value (e.g. duplication)

const shape1 = Object.freeze({
  A: ('value1': 'value1')
});

const shape2 = Object.freeze({
  A: ('othervalue': 'othervalue')
});

(shape1: typeof shape2); // flow error