What am I missing here?

[vagrant inlet]

gencha#0069

Playground Link

Preview:```ts
export interface SQSRecord {
body: string
}

export interface AWSSQSEvent {
Records: SQSRecord[]
}

export type SQSEvent<
TSchema,
TBase extends AWSSQSEvent = AWSSQSEvent

= Omit<TBase, "Records"> & {
Records: Array<Omit<AWSSQSEvent["Records"], "body">
...```

You can choose specific lines to embed by selecting them before copying the link.

[tough dock]

moment

i'mma assume the rubber duck solved this one

!close

[vagrant inlet]

@thick epoch
Because your issue seemed to be resolved, this post was marked as resolved by @tough dock.
If your issue is not resolved, you can reopen this post by running !reopen.
If you have a different question, make a new post in #1057653400046674112.

[tough dock]

well

idk

[thick epoch]

It's not solved 😄

[vagrant inlet]

gencha#0069

Playground Link

Preview:```ts
export interface SQSRecord {
body: string
}

export interface AWSSQSEvent {
Records: SQSRecord[]
}

export type SQSEvent<
TSchema,
TBase extends AWSSQSEvent = AWSSQSEvent

= Omit<TBase, "Records"> & {
Records: Array<Omit<AWSSQSEvent["Records"], "body">
...```

You can choose specific lines to embed by selecting them before copying the link.

[thick epoch]

I'm only getting more confused

!reopen

[tough dock]

ah

apologies, it just looks weird cuz the original message was deleted

[thick epoch]

Yeah, it was only the playground link

[tough dock]

anyway the issue is that it's two separate array types

typescript doesn't merge that into one single array type

[thick epoch]

Hmm aha

[tough dock]

and so when typescript looks up the methods, it looks them up on one of the types

[tough dock]

actually that's because it doesn't really make sense

[thick epoch]

Makes sense

[tough dock]

never mind, i'm thinking about unions

so the actual reason is just that typescript doesn't do it because it doesn't think of every possibility

one way i'd solve it would be to have a generic parameter that goes all the way down to SQSRecord

[thick epoch]

I was about to ask. Sounds good enough for me

[thick epoch]

Thanks 🙂

[vagrant inlet]

n_n#2622

Playground Link

Preview:```ts
...
export interface SQSRecord<T = string> {
body: T
}

export interface AWSSQSEvent<T = string> {
Records: SQSRecord<T>[]
}

export type SQSEvent<
TSchema,
TBase extends AWSSQSEvent<unknown> = AWSSQSEvent<
TSchema extends AWSSQSEvent<infer T> ? T : string

= TBase & TSchema
...```

[tough dock]

something like this

depending on your actual code you may have to modify it a bit of course

[thick epoch]

Sadly, I have no control over AWSSQSEvent. That's from an external library

[tough dock]

😔

is TSchema guaranteed to have Records: { body: something; }[]?

[tough dock]

if so then you could probably just do

interface GeneralSQSRecord {
    body: unknown;
}
interface GeneralAWSSQSEvent {
    Records: GeneralSQSRecord[];
}
export type SQSEvent<TSchema extends GeneralAWSSQSEvent, TBase extends AWSSQSEvent = AWSSQSEvent> = Omit<TBase, "Records"> & TSchema;

otherwise the best (?) solution may be to use a conditional type

export type SQSEvent<TSchema, TBase extends AWSSQSEvent = AWSSQSEvent> =
  TSchema extends GeneralAWSSQSEvent
? Omit<TBase, "Records"> & TSchema
: TBase & TSchema;

[thick epoch]

Yes, kinda. The type is inferred from a JSON schema with https://www.npmjs.com/package/json-schema-to-ts. So the field is in my JSON Schema and is in the inferred type, but it's weird maybe

Let me check out your suggestion, I was just at lunch

Definitely got my brain on the right track. Right now, I'm favoring this:

import { ArrayElement } from "@dynmedia/lib-tools";
import { SQSEvent as AWSSQSEvent } from "aws-lambda";

export type SQSEvent<
  TSchema extends { Records: Array<unknown> },
  TBase extends AWSSQSEvent = AWSSQSEvent
> = Omit<TBase, "Records"> & {
  Records: Array<
    Omit<ArrayElement<AWSSQSEvent["Records"]>, "body"> & ArrayElement<TSchema["Records"]>
  >;
};

[tough dock]

ArrayElement<T> aka T[number]