Function mut

mut<
    const S extends
        | undefined
        | null
        | string
        | number
        | bigint
        | boolean
        | symbol
        | RegExp
        | Date
        | { -readonly [K in string
        | number
        | symbol]: Mut<S[K], RegExp | Date> },
    T,
>(
    l: { -readonly [K in string | number | symbol]: S[K] } & T,
): { -readonly [K in string | number | symbol]: T[K] }

mut<
    const L extends
        | undefined
        | null
        | string
        | number
        | bigint
        | boolean
        | symbol
        | RegExp
        | Date
        | { -readonly [K in string
        | number
        | symbol]: Mut<L[K], RegExp | Date> },
    const R extends
        | undefined
        | null
        | string
        | number
        | bigint
        | boolean
        | symbol
        | RegExp
        | Date
        | { -readonly [K in string
        | number
        | symbol]: Mut<R[K], RegExp | Date> },
    S,
    T,
>(
    l: { -readonly [K in string | number | symbol]: L[K] } & S,
    r: { -readonly [K in string | number | symbol]: R[K] } & T,
): { -readonly [K in string | number | symbol]: (S & T)[K] }