feature request - add uniqueItems and sorted properties to array type

[MarcelOldenkamp]

Similar to the existing properties minLength and minLength add support for properties uniqueItems and sorted.

• Sorted should accept a selector function to specify the value to sort on (perhaps also sort order).
• uniqueItems boolean true (or perhaps an optional selector function to only enforce uniqueness of a specific value)?

With this feature we would no longer need to define custom types like:

/**
 * An array with length > 0 and distinct values.
 * Allows custom comparator function to specify 'distinct' values, defaults to 'isEqual', which performs a deep comparison between two values for equality comparison.
 * Note that although array length is validated, the array element(s) itself may still be falsy (undefined etc.) depending on the elementType.
 * WARNING: Be sure to document the distinct behavior in de OpenApiMetadata of the type you are using this with so API consumers are aware
 * of this restriction
 * @param elementType the type of the array elements.
 */
type NonEmptyDistinctArray<T> = Branded<T[], 'NonEmptyDistinctArray'>;
function NonEmptyDistinctArray<T>(elementType: Type<T>, comparatorFn: Comparator<T> = isEqual): Type<NonEmptyDistinctArray<T>> {
    const type = NonEmptyArray<T>(elementType)
        // Set the brand to plain `NonEmptyDistinctArray`:
        .withConstraint('NonEmptyDistinctArray', value => {
            return uniqWith(value, comparatorFn).length === value.length || 'no duplicate values allowed';
        });
    // But set the runtime name to be more specific:
    Object.defineProperty(type, 'name', { value: `NonEmptyDistinctArray<${elementType.name}>` });
    return type;
}

type NonEmptyDistinctSortedDates<T> = Branded<T[], 'NonEmptyDistinctSortedDates' | 'NonEmptyDistinctArray'>;
function NonEmptyDistinctSortedDates<T extends ISODate>(elementType: Type<T>) {
    const type = NonEmptyDistinctArray<T>(elementType)
        // Set the brand to plain `NonEmptyDistinctSortedDates`:
        .withConstraint('NonEmptyDistinctSortedDates', value => {
            return value.every(pairwise((next, prev) => !prev || next > prev)) || 'should be sorted by date';
        });
    // But set the runtime name to be more specific:
    Object.defineProperty(type, 'name', { value: `SortedByDate<${elementType.name}>` });
    return type;
}

with:

/**
 * An array with length > 0.
 * Note that although array length is validated, the array element(s) itself may still be falsy (undefined etc.) depending on the elementType.
 * @param elementType the type of the array elements.
 */
export function NonEmptyArray<T>(elementType: Type<T>): Type<T[]> {
    return array(elementType).withConfig(`NonEmptyArray<${elementType.name}>`, {
        minLength: 1,
        customMessage: `expected at least one ${elementType.name}`,
    });
}