Add a provable Variant type
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`Variant`s (alternatively known as "sum types", "discriminated unions", or "tagged unions") are a way to define a type that can be one of several different types, but only one at a time. This is useful for representing data that can take on multiple forms, such as for JSON data that can be one of several different types (e.g. a string, number, object, array, etc.).
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Aug 21, 2025
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| static toFields(value: ExactlyOne<Ts>): Field[] { | ||
| const key = getKey(value) as keyof As; | ||
| const typedValue = value as any; |
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Note that this is an internal hack to get this to compile without errors. It is true that if x is keyof ExactlyOne<Ts> then x is keyof As, but I couldn't prove it to typescript easily, so I cast to any here.
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Variants (alternatively known as "sum types", "discriminated unions", or "tagged unions") are a way to define a type that can be one of several different types, but only one at a time. This is useful for representing data that can take on multiple forms, such as for JSON data that can be one of several different types (e.g. a string, number, object, array, etc.).This implementation includes an exported
ExactlyOnetype as well, that represents a single branch of a variant.