Contravariance issue

[timber mason]

sabisenpai#0

Playground Link

Preview:```ts
type QueryConfig<T> = {
getTs: () => Promise<T[]>
filterT?: (t: T) => boolean
doSomethingWithT?: (t: T) => void
}

const aQuery: QueryConfig<{include: boolean}> = {
getTs: async () => [
{include: true},
{include: false},
],
filterT: ({include}) => include
...```

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

[drowsy grove]

What would you fine folks recommend here? 😅

[round kiln]

you can make this typecheck if you give queriesRunner a type parameter:

[timber mason]

mkantor#0

Playground Link

Preview:```ts
...
type Queries<T extends readonly unknown[]> = {
[K in keyof T]: QueryConfig<T[K]>
}

// Simplified usage

const queriesRunner = async <
T extends readonly unknown[]

(
queries: Queries<T>
): Promise<void> => {
await Promise.all(
queries.map(async query => {
const ts = await query.getTs()
const filteredTs = query.filterT
? ts.filter(query.filterT)
: ts
for (const t of filteredTs) {
query.doSomethingWithT?.(t)
}
})
)
}

queriesRunner([aQuery, bQuery])
...```

[round kiln]

although i might consider factoring things this way instead:

[timber mason]

mkantor#0

Playground Link

Preview:```ts
...
const applyQuery = async <T>(
query: QueryConfig<T>
) => {
const ts = await query.getTs()
const filteredTs = query.filterT
? ts.filter(query.filterT)
: ts
for (const t of filteredTs) {
query.doSomethingWithT?.(t)
}
}

Promise.all([applyQuery(aQuery), applyQuery(bQuery)])```

[drowsy grove]

@round kiln I really like the applyQuery! Unfortunately I think I stripped down my example a bit too much 😅 This is closer to reality:

[timber mason]

sabisenpai#0

Playground Link

Preview:```ts
// singleton, consumed by a "router runtime" of sorts
type RouterConfigs = RouterConfig[];

// dozens of these
type RouterConfig = {
services: ServiceConfig[];
}

// hundreds of these
type ServiceConfig = {
// ... existing functionality

newFunctionality?: QueryConfig<unknown>;

...```

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

[drowsy grove]

Applying generics all the way down is probably what I'd do if this was being written from scratch, but retrofitting it in is a massive sweeping change and this new functionality is meant to be completely opt-in, zero changes to anything not using it

[round kiln]

which part of this is the new functionality? filterT and doSomethingWithT? what do the current router configs/services look like?

i'm also generally unsure why/how the new stuff you shared (ServiceConfig, RouterConfig, etc) are relevant. in your original playground you had a queriesRunner function which took multiple QueryConfig objects as input. are you saying that's not what you really need, and instead you want a function to consume RouterConfigs or somesuch?