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Typescript match discriminated union tag
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| type MatchTag = { | |
| // Strict match, one handler must be provided for each possible tag | |
| < | |
| X extends { _tag: string }, | |
| K extends { | |
| [k in X['_tag']]: (member: Extract<X, { _tag: k }>) => any | |
| }, | |
| >( | |
| handlers: K, | |
| ): (member: X) => ReturnType<K[keyof K]> | |
| // Partial match, only provide a handler for the desired tag and handle the rest via a fallback handler | |
| < | |
| X extends { _tag: string }, | |
| K extends Partial<{ | |
| [k in X['_tag']]: (_: Extract<X, { _tag: k }>) => any | |
| }>, | |
| H, | |
| >( | |
| partialHandlers: K & { | |
| [k in X['_tag']]?: (member: Extract<X, { _tag: k }>) => any | |
| }, | |
| fallback: (_: Exclude<X, { _tag: keyof K }>) => H, | |
| ): (member: X) => { [k in keyof K]: ReturnType<NonNullable<K[k]>> }[keyof K] | H | |
| } | |
| /** | |
| * Execute a function for each possible tag of a discriminated union | |
| * | |
| * Basically a more concise & expressive version of doing switch(union._tag) {case "blah": ...} | |
| */ | |
| export const matchTag: MatchTag = ((handlers: any, fallback: any) => (member: any) => { | |
| if (!handlers[member['_tag']]) return fallback(member) as any | |
| return handlers[member['_tag']](member) as any | |
| }) as any |
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