Need implicit casts between Promise<object> and Promise and interfaces

[ericnewton76]

Need some implicit casts for T=object scenarios. I keep running into odd compiler errors of not able to convert from Promise

[ericnewton76]

Just to clarify after thinking about this.

All Promises should still shuttle around an object reference, and that object ref can be null.

So a Then((x) => { Assert.That(x==null) }) on a Promise<object> cast to a Promise. This should work fine, given the following:

var Promise1 = new Promise((resolve,reject) => { resolve(); });
var Promise2 = new Promise<string>((resolve,reject) => { resolve("A"); });
var Promise3 = new Promise<int>((resolve,reject) => { resolve(1); });

Promise.All(Promise1, Promise2, Promise3) 
//Could force this to be Promise<object>.All but realistically that should be the default I think
//but even Promise<object>.All doesnt work because Promise1 cant convert to IPromise<object>
.Then(results => {
  Assert.That(results.ElementAt(0), Is.Null);

  Assert.That(results.ElementAt(1), Is.NotNull);
  Assert.That(results.ElementAt(1), Is.EqualTo("A"));

  Assert.That(results.ElementAt(2), Is.NotNull);
  Assert.That(results.ElementAt(2), 1);
}

Unless I'm not thinking about this correctly... lol

I will probably generate a PR for this, I worry that it'll touch every aspect of the library though.

[ericnewton76]

Just a question, was there a need for the IPromise interfaces? I dont actually see a need for them.

That way, Promise.All takes Promise types instead, and the implicit casts can easily shuttle Promise

[ashleydavis]

It doesn't feel right to me that a promise that yields no value should be able to implicitly cast to a null result.

There are two reasons for the interfaces.

1. Having an interface allows a promise to be mocked.
2. Having two interfaces allows you to seperate your concerns. One interface allows a promise to be awaited, the other allows a promise to be resolved.