// cheap lodash replacements
export function memoize(fn) {
    let result = null;
    const memoized = () => {
        if (result == null) {
            result = fn();
        }
        return result;
    };
    return memoized;
}
/**
 * drop-in replacement for _.without
 */
export function without(items, item) {
    return items.filter(i => i !== item);
}
export function union(itemsA, itemsB) {
    const set = new Set();
    const insertItem = (item) => set.add(item);
    itemsA.forEach(insertItem);
    itemsB.forEach(insertItem);
    const result = [];
    set.forEach(key => result.push(key));
    return result;
}