Add prototype-patching operator modules

[robwormald]

Step one (broken into two commits - operators and statics) in modularization strategy.

Moves prototype patching into individual modules, so Observable prototype can be patched incrementally.

Before:

import {Observable} from '@reactivex/rxjs'; //ALL THE THINGS
//or
import {Observable} from '@reactivex/rxjs/Observable'; //NONE OF THE THINGS

After:

import {Observable} from '@reactivex/rxjs/Observable'; //NONE OF THE THINGS
//SOME OF THE THINGS!
import '@reactivex/rxjs/observables/PromiseObservable';
import '@reactivex/rxjs/operators/map';
import '@reactivex/rxjs/operators/filter';
import '@reactivex/rxjs/operators/reduce';

Part two will be using TS 1.8's module-reopening functionality to patch the interface, at which point the stub methods will be removed from Observable.ts. Not implemented yet - see microsoft/TypeScript#5269 (comment)

Current side effect (minor) is that type-completion will show methods that have possibly not been imported yet.

Closes #750

[robwormald]

cc @IgorMinar @jeffbcross - i couldn't work out optional syntax here, might be the pumpkin pie hangover.

[benlesh]

//SOME OF THE THINGS!
import '@reactivex/rxjs/observables/PromiseObservable';

This confuses me. Is this to say that fromPromise doesn't exist until PromiseObservable is imported? While I'm generally in favor of this approach for operators. I think for the static methods it's harder to figure out.

[benlesh]

Perhaps it should be:

import `@reactivex/rxjs/observable/fromPromise`;

(NOTE: The reactivex/rxjs will shrink to just rxjs at some point)

[robwormald]

Yes, correct, it doesn't exist until imported.

Definitely like this better, it reads much more nicely 👍

import `@reactivex/rxjs/observable/fromPromise`;

[benlesh]

I'd go so far as to have it also export the fromPromise function (same for the others).

So:

import {fromPromise} from 'rxjs/observable/fromPromise';

fromPromise(makePromise()).subscribe();

or

import {Observable} from 'rxjs/observable';
import 'rxjs/observable/fromPromise';

Observable.fromPromise(makePromise()).subscribe();

would both work.

[benlesh]

... well I guess it could export PromiseObservable... I dunno. As long as the name is easier to read.

[trxcllnt]

@Blesh:
I'd go so far as to have it also export the fromPromise function (same for the others). [snip] ... well I guess it could export PromiseObservable... I dunno. As long as the name is easier to read.

Could we export both fromPromise and PromiseObservable from that module, or would that go against our "only export one thing per module" rule?

[benlesh]

Could we export both fromPromise and PromiseObservable from that module, or would that go against our "only export one thing per module" rule?

No such rule, IMO. So I don't see why not.

[robwormald]

observables => observable ✔️

[benlesh]

LGTM.

[benlesh]

Merged as of 95279cc... VERY nice work, @robwormald, and great idea overall @IgorMinar @jeffbcross et al.

[kwonoj]

👍 yay!

[robwormald]

@trxcllnt i like the idea of exporting fromPromise et al, but they're mostly static methods on classes (PromiseObservable.create) - should i just

const fromPromise = PromiseObservable.create;
export {fromPromise}

or is there something more clever i'm missing?