#How do I forward the tupleness to another type-argument? (two array types of the same length)

11 messages · Page 1 of 1 (latest)

nova sail
#

Here is the playground link:

vocal dragonBOT
#
[vFp] NullVoxPopuli#0001
Playground Link

Preview:```ts
export interface MappedArray<MappedTo> {
[index: number]: MappedTo
values: () => readonly MappedTo[]
length: number
Symbol.iterator: Iterator<MappedTo>
}

export function map<Element, MapTo>(options: {
data: () => readonly El
...```

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stuck bloom
#

@nova sail the issue is that it's impossible for the return type of map.data to be a tuple...

#

since you explicitly define it to be an array

nova sail
#

how do I explicitly define it to be a tuple?

vocal dragonBOT
stuck bloom
#

!ts

vocal dragonBOT
# 
export interface MappedArray<Arr extends readonly unknown[], MappedTo> {
  [index: number]: MappedTo;
  values: () => { [K in keyof Arr]: MappedTo };
  length: number;
  [Symbol.iterator](): Iterator<MappedTo>;
}

export function map<Arr extends readonly unknown[], MapTo>(
  options: {
    data: () => Arr;
    map: (element: Arr[number]) => MapTo;
  }
) {
  /**
    actual implementation omitted
   */
  return options.data as unknown as MappedArray<Arr, MapTo>;
}



function doubleEach<T extends readonly number[]>(input: T): T {
	return input.map(i => i * 2) as unknown as T;
}

function doubleEachFn<T extends readonly number[]>(input: () => T): T {
	return input().map(i => i * 2) as unknown as T;
}

function doubleEachFn2<T, Arr extends readonly T[]>(input: () => Arr): Arr {
  // implementation not important
	return input().map((i: any) => i * 2) as unknown as Arr;
}

const original = [1, 2, 3, 4] as const;

let result: number = doubleEach(original)[0];
let result2: number = doubleEachFn(() => original)[0];
let result3: number = doubleEachFn2(() => original)[0];
let result4: number = map({ data: () => original, map: (num) => num * 2 }).values()[0];
nova sail
#

🤔

gusty trout
#

I am unsure of what you intended with your original code, could you provide what you expected to get back on your result variables from your function calls?

nova sail
#

I figured it out, actually 🙃