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Improvment to Array.isArray #151

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Improvment to Array.isArray #151

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ab9d475
Fixes to isArray
Mickemouse0 Jun 17, 2023
d2918bb
Update is-array.d.ts
Mickemouse0 Jun 17, 2023
710e603
Improve readability
Mickemouse0 Jun 20, 2023
db19046
Fix indentation
Mickemouse0 Jun 20, 2023
4be3b4f
Remove invalid test
Mickemouse0 Jun 23, 2023
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2 changes: 1 addition & 1 deletion src/entrypoints/is-array.d.ts
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@@ -1,3 +1,3 @@
interface ArrayConstructor {
isArray(arg: any): arg is unknown[];
isArray<T>(arg: true extends TSReset.IsAny<T> ? never : T): arg is true extends TSReset.IsAny<T> ? never : T extends ReadonlyArray<unknown> ? T : Array<T> extends T ? Array<T> : never;
}
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Not sure I agree with the decision to disallow any, since narrowing a value from any to unknown[] seems like a valid thing to want to do.

Setting that aside, here's another way you could accomplish the same thing:

Suggested change
interface ArrayConstructor {
isArray(arg: any): arg is unknown[];
isArray<T>(arg: true extends TSReset.IsAny<T> ? never : T): arg is true extends TSReset.IsAny<T> ? never : T extends ReadonlyArray<unknown> ? T : Array<T> extends T ? Array<T> : never;
}
interface ArrayConstructor {
isArray<T>(arg: NotAny<T>): arg is Extract<NotAny<T>, readonly unknown[]>;
}
type NotAny<T> = 0 extends 1 & T ? never : T

3 changes: 3 additions & 0 deletions src/entrypoints/utils.d.ts
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Expand Up @@ -14,4 +14,7 @@ declare namespace TSReset {
: T extends symbol
? symbol
: T;

// https://stackoverflow.com/questions/49927523/disallow-call-with-any/49928360#49928360
type IsAny<T> = 0 extends 1 & T ? true : false;
}
82 changes: 81 additions & 1 deletion src/tests/is-array.ts
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Expand Up @@ -8,6 +8,30 @@ doNotExecute(() => {
}
});

doNotExecute(() => {
const maybeArr = [1, 2, 3] as unknown[];

if (Array.isArray(maybeArr)) {
type tests = [Expect<Equal<typeof maybeArr, unknown[]>>];
}
});

doNotExecute(() => {
const maybeArr = [1, 2, 3] as any;

if (Array.isArray(maybeArr)) {
type tests = [Expect<Equal<typeof maybeArr, any[]>>];
}
});

doNotExecute(() => {
const maybeArr = [1, 2, 3] as any[];

if (Array.isArray(maybeArr)) {
type tests = [Expect<Equal<typeof maybeArr, any[]>>];
}
});

doNotExecute(() => {
const arrOrString = [] as string[] | string;

Expand All @@ -17,9 +41,65 @@ doNotExecute(() => {
});

doNotExecute(() => {
let path: string | string[] = [];
const arrOrString = [] as readonly string[] | string;

if (Array.isArray(arrOrString)) {
type tests = [Expect<Equal<typeof arrOrString, readonly string[]>>];
}
});

doNotExecute(() => {
const arrOrString = [] as readonly string[] | string[] | string;

if (Array.isArray(arrOrString)) {
type tests = [Expect<Equal<typeof arrOrString, readonly string[] | string[]>>];
}
});

doNotExecute(() => {
const arrOrString = [] as string[] | string;

if (Array.isArray(arrOrString)) return;
type tests = [Expect<Equal<typeof arrOrString, string>>];
});

doNotExecute(() => {
const arrOrString = [] as readonly string[] | string;

if (Array.isArray(arrOrString)) return;
type tests = [Expect<Equal<typeof arrOrString, string>>];
});

doNotExecute(() => {
const arrOrString = [] as readonly string[] | string[] | string;

if (Array.isArray(arrOrString)) return;
type tests = [Expect<Equal<typeof arrOrString, string>>];
});

doNotExecute(() => {
let arrOrString = "" as string | [1, 2];

if (Array.isArray(arrOrString)) {
type tests = [Expect<Equal<typeof arrOrString, [1, 2]>>];
}
});

doNotExecute(() => {
let path = [] as string | string[];

const paths = Array.isArray(path) ? path : [path];

type tests = [Expect<Equal<typeof paths, string[]>>];
});

doNotExecute(() => {
function test<T>(value: T) {
type Unarray<T> = T extends Array<infer U> ? U : T;
const inner = <X extends Unarray<T>>(v: X[]) => {};

if (Array.isArray(value)) {
inner(value);
}
}
});