31 lines
1.2 KiB
TypeScript
31 lines
1.2 KiB
TypeScript
// Copyright 2021 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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/**
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* Turn a string (like "green") into its enum type (like `Color.Green`). Useful when
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* deserializing strings into enum types.
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*
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* It only supports enums with string values. It could theoretically support more, but:
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*
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* 1. It's easier to debug. A serialized value of "Green" is easier to associate with
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* `Color.Green` than a serialized value of 2.
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* 2. TypeScript's default uses numeric enum values. Because the stability of values is
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* important and it's easy to mess up the stability of values (e.g., by reordering the
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* enum), these are discouraged here.
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*
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* Again: no "hard" technical reason why this only supports strings; it's to encourage
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* good behavior.
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*/
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export function makeEnumParser<
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TEnumKey extends string,
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TEnumValue extends string
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>(
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enumToParse: Record<TEnumKey, TEnumValue>,
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defaultValue: TEnumValue
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): (value: unknown) => TEnumValue {
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const enumValues = new Set(Object.values(enumToParse));
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const isEnumValue = (value: unknown): value is TEnumValue =>
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typeof value === 'string' && enumValues.has(value);
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return value => (isEnumValue(value) ? value : defaultValue);
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}
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