Allow inferred type exporting and/or acquiring the type of a function returned value

[wkrueger]

Hello. I'm currently writing an Angular1 app and trying to avoid the use of classes. But sometimes it seems a reasonable type-checking can only be achieved either by re-defining the "methods" via interfaces, or by using classes. Let's talk examples:

function SomeService( $someInject ) {
    $someInject.run()
    //will use this later
    var out = {
        doThis() { return 22 },
        doThat() { return 'cool'}
    }
    return out
}

function SomeConsumer( $scope , SomeService:WhatType ) {
    $scope.values = SomeService.doThis()
}

While out has an inferred type inside its function scope, I can't access it outside. While inside the function I can get type MyService = typeof out, MyService isn't accessible outside.

Another way to get the desired result there would be to fetch the type of the function returned value. Something like type MyService = typeof SomeService().

Currently my only options seem to be:
either using class style:

class SomeService {
    constructor(private $someInject) { }
    doThis() {
        this.$someInject.run()
       return 22
    }
}
function consumer(SomeService:SomeService) {
  //...
}

or by redefining the methods in an interface (+keystrokes)

interfase SomeService {
    doThis : () => number;
    doThat : () => number;
}

[wkrueger]

Related:
#4233
#6606
my bad, should have commented it there