Define Array.isArray using a type predicate #3492
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| @@ -1150,7 +1150,7 @@ interface ArrayConstructor { | |||
| (arrayLength?: number): any[]; | |||
| <T>(arrayLength: number): T[]; | |||
| <T>(...items: T[]): T[]; | |||
| isArray(arg: any): boolean; | |||
| isArray(arg: any): arg is Array<any>; | |||
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could we allow this to be generic? i.e.
isArray<T>(arg: any): arg is Array<T>?
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We could, but we should add a separate overload for it. Otherwise, not passing the type argument gives you Array<{}>
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so are you expecting this to work:
var arr: Array<number> | Array<string>;
if (Array.isArray<number>(arr)) {
arr[0].toFixed(); // but what does that mean at runtime?
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@mhegazy I think you're right. Specifying the type is claiming to know something that you don't.
mhegazy
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Jun 13, 2015
Define Array.isArray using a type predicate
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With type predicates in, here is a change to the lib to make it use that in isArray definition.