export type Selection = 'all' | Set<Key>;

export interface MultipleSelection {
  /** The type of selection that is allowed in the collection. */
  selectionMode?: SelectionMode,
  /** Whether the collection allows empty selection. */
  disallowEmptySelection?: boolean,
  /** The currently selected keys in the collection (controlled). */
  selectedKeys?: 'all' | Iterable<Key>,
  /** The initial selected keys in the collection (uncontrolled). */
  defaultSelectedKeys?: 'all' | Iterable<Key>,
  /** Handler that is called when the selection changes. */
  onSelectionChange?: (keys: Selection) => any,
  /** The currently disabled keys in the collection (controlled). */
  disabledKeys?: Iterable<Key>
}

class ... extends Set {
    constructor(keys, anchorKey, currentKey){
        super(keys);
        if (keys instanceof ...) {
            this.anchorKey = anchorKey || keys.anchorKey;
            this.currentKey = currentKey || keys.currentKey;
        } else {
            this.anchorKey = anchorKey;
            this.currentKey = currentKey;
        }
    }
}

/*
 * Copyright 2020 Adobe. All rights reserved.
 * This file is licensed to you under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License. You may obtain a copy
 * of the License at http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under
 * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
 * OF ANY KIND, either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

import {Key} from '@react-types/shared';

/**
 * A Selection is a special Set containing Keys, which also has an anchor
 * and current selected key for use when range selecting.
 */
export class Selection extends Set<Key> {
  anchorKey: Key;
  currentKey: Key;

  constructor(keys?: Iterable<Key> | Selection, anchorKey?: Key, currentKey?: Key) {
    super(keys);
    if (keys instanceof Selection) {
      this.anchorKey = anchorKey || keys.anchorKey;
      this.currentKey = currentKey || keys.currentKey;
    } else {
      this.anchorKey = anchorKey;
      this.currentKey = currentKey;
    }
  }
}

<Dropdown>
        <DropdownTrigger>
          <div>
            Test
          </div>
        </DropdownTrigger>
        <DropdownMenu
          aria-label="Single selection example"
          variant="flat"
          disallowEmptySelection
          selectionMode="single"
          selectedKeys={selectedKeys}
          onSelectionChange={handleOnDropdownChange}
        >
          {generateList()}
        </DropdownMenu>
</Dropdown>