typing in helpers in db-ivm

Hey! I'm using db-ivm to aggregate events from an event-sourced system for display. Working great so far! I've noticed a lot of boilerplate around sorting and filtering, though, and so I've tried to make myself a helper:

export function build<Event extends { timestamp: number }, Out, Key extends string | number>(
  builder: (events: Event[]) => Out | null | undefined,
) {
  return reduce<Key, Event, Out, Keyed<Key, Event>>((events: [Event, number][]) => {
    const res = builder(
      events
        .filter(([_, mult]) => mult === 1)
        .map(([ev, _]) => ev)
        .toSorted((a, b) => a.timestamp - b.timestamp),
    )

    if (res) {
      return [[res, 1]]
    } else {
      return []
    }
  })
}

export function build<Event extends { timestamp: number }, Out, Key extends string | number>(
  builder: (events: Event[]) => Out | null | undefined,
) {
  return reduce<Key, Event, Out, Keyed<Key, Event>>((events: [Event, number][]) => {
    const res = builder(
      events
        .filter(([_, mult]) => mult === 1)
        .map(([ev, _]) => ev)
        .toSorted((a, b) => a.timestamp - b.timestamp),
    )

    if (res) {
      return [[res, 1]]
    } else {
      return []
    }
  })
}

This works fine, except that I have to manually specify the type parameters or they're inferred to be

never

never

. For example, the type params in this call are required:

build<
  QuestionTitleSetV1 | QuestionAddedV1,
  { title: string; type: QuestionAddedV1['data']['type'] },
  string
>((events) => {
  // …
})

build<
  QuestionTitleSetV1 | QuestionAddedV1,
  { title: string; type: QuestionAddedV1['data']['type'] },
  string
>((events) => {
  // …
})

I see an

addOperator

addOperator

call to graph—is that a better way to add helpers like this? Otherwise, any tips on getting type inference working correctly?

typing in helpers in db-ivm

export function build<Event extends { timestamp: number }, Out, Key extends string | number>(
  builder: (events: Event[]) => Out | null | undefined,
) {
  return reduce<Key, Event, Out, Keyed<Key, Event>>((events: [Event, number][]) => {
    const res = builder(
      events
        .filter(([_, mult]) => mult === 1)
        .map(([ev, _]) => ev)
        .toSorted((a, b) => a.timestamp - b.timestamp),
    )

    if (res) {
      return [[res, 1]]
    } else {
      return []
    }
  })
}

export function build<Event extends { timestamp: number }, Out, Key extends string | number>(
  builder: (events: Event[]) => Out | null | undefined,
) {
  return reduce<Key, Event, Out, Keyed<Key, Event>>((events: [Event, number][]) => {
    const res = builder(
      events
        .filter(([_, mult]) => mult === 1)
        .map(([ev, _]) => ev)
        .toSorted((a, b) => a.timestamp - b.timestamp),
    )

    if (res) {
      return [[res, 1]]
    } else {
      return []
    }
  })
}

This works fine, except that I have to manually specify the type parameters or they're inferred to be

never

never

. For example, the type params in this call are required:

build<
  QuestionTitleSetV1 | QuestionAddedV1,
  { title: string; type: QuestionAddedV1['data']['type'] },
  string
>((events) => {
  // …
})

build<
  QuestionTitleSetV1 | QuestionAddedV1,
  { title: string; type: QuestionAddedV1['data']['type'] },
  string
>((events) => {
  // …
})

I see an

addOperator

addOperator

call to graph—is that a better way to add helpers like this? Otherwise, any tips on getting type inference working correctly?

typing in helpers in db-ivm

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