Using 'Key in keyof ArrayType' always returns an Array regardles of the value manipulation applied

TypeScript Version: 4.0.0-beta (same behaviour in version 3.5.1 v3.5.1-Play Ground)

Search Terms:
"key in keyof Array", "keyof Array"

Expected behavior:
using key in ArrayType has the same behaviour as on any object (returning an array type only if the relevant properties are unchanged)

Actual behavior:
using key in ArrayType performs actions on touple entries but the returned type allways includes all default Array properties

Extention note:
Not the point of this issue and i know there are other issues around this topic. it's just a note,
but how about possibly adding tupple functionality for ArrayLike-, Map- and Set-types? They have all the basic qualities of a tupple, and it would be awesome to use them in a similar fashion (especially inference of Map.prototype.get/set and [Symbol.iterator] inference of tupples)

Related Issues:
#39726
#34780
type-fest/issues/119 (external library, but about this this behaviour and includes adHoc fix)

Code

type Arr = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
type Arr2 = (0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9)[]
type WhoopMyArray_Faulty<Base extends ArrayLike<any>, Condition> = {  
		[Key in keyof Base]:
			Base[Key] extends Condition
				? 'Whoop it'
				: Base[Key] extends Base[number] ? Base[Key] : never
	}

// action is performed on array elements but return type is still a proper array
type WhoopedArray = WhoopMyArray_Faulty<Arr, 7 | 5 | 2>
type WhoopedArrayKeys = WhoopMyArray_Faulty<Arr, 7 | 5 | 2>[keyof Arr]

// related side note, but not the main pont
// no action performed. in line with 1st example, expected: (0 | 1 | 'Whoop it' | 3 | 4 | 'Whoop it' | 6 | 'Whoop it' | 8 | 9)[]
type WhoopedArray2 = WhoopMyArray_Faulty<Arr2, 7 | 5 | 2>
type WhoopedArray2Keys = WhoopMyArray_Faulty<Arr, 7 | 5 | 2>[keyof Arr]

infered types:

type WhoopedArray = [0, 1, "Whoop it", 3, 4, "Whoop it", 6, "Whoop it", 8, 9]

type WhoopedArrayKeys = 0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9 | 10 | (() => string) | (() => string) 
  | (() => 0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9 | undefined) | ((...items: (0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9)[]) => number)
  | {    ...;    } | ... 22 more ... | (() => IterableIterator<...>)

type WhoopedArray2 = (0 | 7 | 5 | 2 | 1 | 3 | 4 | 6 | 8 | 9)[]

type WhoopedArray2Keys = 0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9 | 10 | (() => string) | (() => string)
  | (() => 0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9 | undefined) | ((...items: (0 | "Whoop it" | 1 | 3 | 4 | 6 | 8 | 9)[]) => number)
| {     ...;    } | ... 22 more ... | (() => IterableIterator<...>)

"use strict";

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": true,
    "alwaysStrict": true,
    "allowUnusedLabels": true,
    "noEmitHelpers": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "preserveConstEnums": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "moduleResolution": 2,
    "target": "Latest",
    "module": "ESNext"
  }
}

Playground Link: Provided

Commencez par le lien fourni vers TypeScript Playground et les exemples de types mappés utilisant keyof Array et des types tuple. Comparez les types inférés avec le comportement attendu et réel indiqué, puis examinez les issues associées #39726 et #34780. La tâche est terminée lorsque le type mappé conserve les transformations prévues des éléments de tuple ou de Array sans inclure de manière inattendue des membres de Array inchangés.