<?php
namespace {
    class ReflectionClass implements Reflector {
        /** @psalm-pure */
        public function isReadOnly(): bool {}
    }

    /** @psalm-immutable */
    class ReflectionUnionType extends ReflectionType {
        /** @return non-empty-list<ReflectionNamedType|ReflectionIntersectionType> */
        public function getTypes(): array {}
    }

    /**
    * @psalm-immutable
    *
    * @template-covariant Start of string|DateTimeInterface
    * @implements IteratorAggregate<int, DateTimeInterface>
    */
    class DatePeriod implements IteratorAggregate
    {
        const EXCLUDE_START_DATE = 1;
        const INCLUDE_END_DATE = 2;

        /**
        * @param Start $start
        * @param (Start is string ? int-mask<self::EXCLUDE_START_DATE, self::INCLUDE_END_DATE> : DateInterval) $interval
        * @param (Start is string ? never : (DateTimeInterface|positive-int)) $end
        * @param (Start is string ? never : int-mask<self::EXCLUDE_START_DATE, self::INCLUDE_END_DATE>) $options
        */
        public function __construct($start, $interval = 0, $end = 1, $options = 0) {}

        /** @psalm-return (Start is string ? Iterator<int, DateTime> : Iterator<int, Start>) */
        public function getIterator(): Iterator {}
    }
}