Type Alias RequireExactlyOne<T, K>

RequireExactlyOne: {
    [P in K]: Required<Pick<T, P>> & Partial<Record<Exclude<K, P>, never>> & Omit<
        T,
        K,
    >
}[K]

Require exactly one property from a set.

Type Parameters

T
Source object type
K extends keyof T = keyof T
Keys where exactly one must be present (defaults to all keys)

Remarks

Produces a union of object variants where exactly one of the specified properties is present and all others are explicitly disallowed.

Example

type Test = { a?: string; b?: number; c: boolean };
type Result = RequireExactlyOne< Test, 'a' | 'b' >;
// { a: string; b?: never; c: boolean } | { a?: never; b: number; c: boolean }