Enum implementation in PHP

enum.php

<?php
	abstract class Enum {
		private static $cache = [];

		// Helper function to load the required fields into the cache.
		private static function loadCache(): void {
			// Create cache for enum
			self::$cache[static::class] = [];

			// Get all constants
			$refl = new \ReflectionClass(static::class);
			$consts = $refl->getConstants();

			// Store constants in cache
			// NOTE: The value of the constant is ignored
			foreach (array_keys($consts) as $i => $key) {
				self::$cache[static::class][$key] = new static($i, $key);
			}
		}


		// Enum::A() should give Enum::$cache[Enum::A]
		public static function __callStatic(string $name, $_): self {
			// Make sure the cache is loaded
			if (! isset(self::$cache[static::class])) {
				static::loadCache();
			}

			// Check if key exists
			if (! isset(self::$cache[static::class][$name])) {
				throw new \Exception("Invalid key: '$name'");
				return null;
			}

			// Return item from cache
			return self::$cache[static::class][$name];
		}


		// Enum::from('A') should give Enum::$cache[Enum::A]
		public static function from(string $key): self {
			return static::$key();
		}


		private $val;
		private $name;
		private function __construct(int $val, string $name) {
			$this->val = $val;
			$this->name = $name;
		}

		public function __toString(): string {
			return static::class . ' {' . $this->name . '}';
		}

		public function name(): string {
			return $this->name;
		}

		public function val(): int {
			return $this->val;
		}


		public function __debugInfo(): array {
			return [
				'name' => $this->name,
				'val' => $this->val,
			];
		}
	}


	class Month extends Enum {
		const January = null;
		const February = null;
		const March = null;
		const April = null;
		const May = null;
		const June = null;
		const July = null;
		const August = null;
		const September = null;
		const October = null;
		const November = null;
		const December = null;
	}

	class Weekday extends Enum {
		const Monday = null;
		const Tuesday = null;
		const Wednesday = null;
		const Thursday = null;
		const Friday = null;
		const Saturday = null;
		const Sunday = null;
	}


	function planDate(Month $month, Weekday $day) {
		if ((
			// month between january and april
			Month::January()->val() <= $month->val()
			&& $month->val() <= Month::April()->val()
		) || (
			// month between october and december
			Month::October()->val() <= $month->val()
			&& $month->val() <= Month::December()->val()
		))
		{
			return "Sorry, but then it's too cold outside.";
		}

		if ($day == Weekday::Friday()) {
			return "Sorry, I already have an important meeting.";
		}

		return "A " . $day->name() . " in " . $month->name() . " sounds nice!";
	}


	echo planDate(Month::March(), Weekday::Monday()) . "\n";
	echo planDate(Month::from("August"), Weekday::Friday()) . "\n";
	echo planDate(Month::from("June"), Weekday::from("Sunday")) . "\n";