Creating an interface with a symbol?

[benlesh]

TypeScript Version:

1.7.5 / 1.8.0-beta / nightly (1.9.0-dev.20160217)

Code

// try augmenting the SymbolContructor to have some expected symbol on it.
// in RxJS5's case, it'll be the Symbol.observable symbol from the es-observable spec.
interface SymbolConstructor {
  observable: symbol;
}

interface Observablesque<T> {
  [Symbol.observable]: () => Subscribable<T>
}

or

// try importing some symbol reference (I get why this might not work)
import {$$observable} from './symbol/observable';

interface Observablesque<T> {
  [$$observable]: () => Subscribable<T>
}

Expected behavior:

I should be able to enforce types that have symbols on them, custom or otherwise.

Actual behavior:

I get really confused and go get myself a coffee.

[benlesh]

Also, depending on the environment, that interface could be Symbol.observable or it could be '@@observable'.

[benlesh]

What I"m looking at here are specifically two future built-ins: Symbol.observable and Symbol.asyncIterator.

[mhegazy]

The first one should work as if you have the Symbol definition.

The second one is a bit more involved. the issue is we do not know what the import points to at the time when we are building types, there is more discussion in: #2012
the issue is tracked by #5579

[david-driscoll]

Keep in mind, when imported through node definitions, the TypeScript compiler raises an error, because you cannot have ambient references as part of your source (/// <reference path=".../symbol.d.ts" />). Is there a way to augment ambient interfaces?

We had this at one point but it was causing errors so we backed it out.
ReactiveX/rxjs@d185ff8

[mhegazy]

why not declare global?

declare global {
   SymbolConstructor {
     observable: symbol;
   }
}

[benlesh]

why not declare global?

Because I'm a better JavaScript developer than I am a TypeScript expert?

[DanielRosenwasser]

Because I'm a better JavaScript developer than I am a TypeScript expert?

Good point @Blesh - I just filed this issue.

[david-driscoll]

because I didn't know that existed... I'll have to mess with that in a day or two. Thanks!

[benlesh]

No dice with declare global.

[DanielRosenwasser]

@Blesh can you elaborate what issues you're running into? This works for me.

foo.ts

export {};

declare global {
    interface SymbolConstructor {
        observable: symbol;
        asyncIterator: symbol;
    }
}

Symbol.observable;

tsconfig.json

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es6",
        "noImplicitAny": false,
        "sourceMap": false
    },
    "files": [
        "foo.ts"
    ]
}

[benlesh]

@DanielRosenwasser

It complains at me:

TS2665: Module augmentation cannot introduce new names in the top level scope.

[DanielRosenwasser]

SymbolConstructor will need to have been declared somewhere, so if you'll need to target ES6 or have a .d.ts file that declares it.

I believe if you're using nightlies, you could avoid targeting ES6 and use --lib es6.

[mhegazy]

logged #8102 for the error.

[benlesh]

I believe if you're using nightlies, you could avoid targeting ES6 and use --lib es6.

What is this and how does it benefit us?

[robwormald]

@Blesh the nightly versions of TS let you do:

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es5",
        "noImplicitAny": false,
        "sourceMap": false,
        "outDir": "dist",
        "lib": ["es5", "es2015.promise", "dom"]
    },
    "files": [
        "src/main.ts"
   ]
}

rather than providing say, es6-shim external defs (the above config is what's needed to use rxjs, currently)

@DanielRosenwasser while Observable isn't part of the es6/es7 scope, its currently a stage1 proposal... does the lib option (amaaazing) provide a facility to add external lib.whatever files, or might y'all be open to having a lib.stage1.d.ts etc option as part of TS?

[mhegazy]

closing in favor of #5579