Support user defined type guards in filter predicates

[OliverJAsh]

IxJS version:
2.1.0

Code to reproduce:

// no error, good!
// TypeScript's Array typings support user defined type guards in the filter predicate
const xs: number[] = ['foo', 1].filter((x): x is number => x instanceof Number);

// unexpected error
const xs2: Ix.Iterable<number> = Ix.Iterable
    .from(['foo', 1])
    .filter((x): x is number => typeof x === 'number');

[ichpuchtli]

wow I didn't know that that's awesome.

[trxcllnt]

@OliverJAsh 🎉 thanks!

[OliverJAsh]

@trxcllnt Using 2.1.4, the example above still seems to generate an error. Any ideas?

[trxcllnt]

@OliverJAsh I don't think they made it in the 2.1.4 release, will circle back with @mattpodwysocki and do another release soon

[trxcllnt]

@OliverJAsh just pushed this out in 2.2.0, but also be aware of this breaking change to zip when you update

[OliverJAsh]

I'm using 2.2.0 and the example above still seems to generate an error. Any ideas? @trxcllnt

❯ grep version node_modules/ix/package.json
  "version": "2.2.0",

[trxcllnt]

@OliverJAsh oh you're right, looks like I forgot to extend the generic type:

edit hm this is weird. trying to figure it out, gimme a bit.

There's still the issue that 1 instanceof Number evaluates to false, so the runtime behavior won't be what you expect even though TS gives the OK. I ran into that in the type guards test

[OliverJAsh]

Thanks for the fix @trxcllnt. I'll give it another go once it's released.

There's still the issue that 1 instanceof Number evaluates to false

I've updated the example in the original post now.

[OliverJAsh]

@trxcllnt Thanks for fixing this! My original example now works (ix 2.3.1), however this doesn't:

// no error, good!
const xs2: Ix.Iterable<number> = Ix.Iterable
    .from(['foo', 1])
    .filter((x): x is number => typeof x === 'number')

// no error, good!
const xs2b: Ix.Iterable<number> = xs2.map(x => x);

// unexpected error, bad!
const xs3: Ix.Iterable<number> = Ix.Iterable
    .from(['foo', 1])
    .filter((x): x is number => typeof x === 'number')
    .map(x => x)

Any ideas what is causing this?

[OliverJAsh]

I opened a separate issue to track the above #162