dphilipson / transducist Goto Github PK

TansformationChain.flatten: void

This expression is not callable. Type 'void' has no call signatures.

.flatten appears to be wrongly typed

Code example:

chainFrom(someData)
.filter(({ prop }) => prop)
.map(({ prop }) => prop * 2)
.flatten() // Error
.toArray()

If there a type guard function is passed to the filter in the transducer, the resulting inferred type does not respect the type guard, unlike the native filter function. It works with explicit typing, but that is obviously cumbersome in more complex situations.

import { map, filter, transduce, compose, toArray } from 'transducist'

const k: Array<number | undefined> = [1, 2, undefined]

const l = transduce(
  k,
  compose(
    filter((i: number | undefined): i is number => i !== undefined),
    map((i) => i * 2) // Error: i  is possibly undefined
  ),
  toArray()
)

const r = k
  .filter((i: number | undefined): i is number => i !== undefined)
  .map((i) => i * 2) // No error