Simplify the Observable pipe with the help of Typescript Variadic Functions about rxjs

[vitaly-t]

I like this idea!

Perhaps because it is your own idea? 🥲 Perhaps you like all your ideas? 🥲

P.S. I like my comment!

[voliva]

@hansschenker sorry I did a 👎 without giving a reason.

The pipe operator is not using TS' variadic arguments and is using many overloads instead because it needs to have some properties that, at least on the previous TS versions, it was impossible to achieve.

You need to have a pipe function that can automatically infer the value of each Operator within the chain, as well as find incompatibilities:

from([1,2,3]).pipe(
  map(v => {
    // TS knows v is a number, so you can run .toFixed() on it
    return v.toFixed();
  }),
  switchMap(v => {
    // TS knows v is a string
    ...
  })
);

There has been multiple attempts at leveraging TS variadic types to simplify that and also allow for a potentially infinite amount of arguments, but so far it has been just not possible to do. Probably the most advanced one was #6671, unfortunately he removed the gist, but it did allow an arbitrary amount of arguments and it would check that every type matches. The problem was that you had to manually fill in all of the type annotations and it would just perform the check, throwing a "is not assignable to never" in case it failed.

Your proposed solution:

// Define a type alias for variadic functions
type PipeFunctions<T> = [(source: Observable<T>) => any, ...Array<UnaryFunction<any, any>>];

is just using any everywhere, so no inference will be done and no type checking will happen whatsoever.

[hansschenker]

I like this idea!