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29 lines
1.2 KiB
TypeScript
29 lines
1.2 KiB
TypeScript
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
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/**
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* Checks if the actual type `A` is assignable to the expected type `E`, and
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* vice versa.
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*
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* This is often less strict than `IsExact` because the two type parameters are
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* allowed to have a different structure as long as they are assignable to each
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* other. This is often more strict than `Has` because none of the two type
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* parameters may be a union that contains the other, as this would fail the
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* check for mutual assignability.
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*
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* @example Usage
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* ```ts
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* import { assertType } from "@std/testing/types";
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* import type { IsMutuallyAssignable } from "@std/testing/unstable-types";
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*
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* // false because E is not assignable to A
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* assertType<IsMutuallyAssignable<string & RegExpMatchArray, string>>(false);
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* // false because A is not assignable to E
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* assertType<IsMutuallyAssignable<string | RegExpMatchArray, string>>(false);
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* // true because both types are assignable to each other
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* assertType<IsMutuallyAssignable<string | (string & RegExpMatchArray), string>>(true);
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* ```
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*/
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export type IsMutuallyAssignable<A, E> = [E] extends [A]
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? [A] extends [E] ? true : false
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: false;
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