diff --git a/composer.json b/composer.json
index 2aa293c..63b8f16 100644
--- a/composer.json
+++ b/composer.json
@@ -1,6 +1,6 @@
 {
     "name": "intraworlds/enum",
-    "description": "Lightweight implementation of enum value object in PHP.",
+    "description": "Lightweight implementation of enum value object",
     "type": "library",
     "require-dev": {
         "phpunit/phpunit": "^7.4"
@@ -12,6 +12,11 @@
             "email": "ondrej.esler@intraworlds.com"
         }
     ],
+    "autoload": {
+        "psr-4": {
+            "IW\\": "src"
+        }
+    },
     "require": {
         "php": ">=7.1"
     }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
new file mode 100644
index 0000000..24927f4
--- /dev/null
+++ b/phpunit.xml.dist
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit colors="true">
+    <testsuites>
+        <testsuite>
+            <directory>tests/</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>
diff --git a/src/Enum.php b/src/Enum.php
new file mode 100644
index 0000000..e91d760
--- /dev/null
+++ b/src/Enum.php
@@ -0,0 +1,155 @@
+<?php declare(strict_types=1);
+
+namespace IW;
+
+/**
+ * Base for enum-like value object, it defines static methods with same names as constants which returns singleton
+ * of particular enum and its value.
+ *
+ * Implementation is simpler version of library https://packagist.org/packages/myclabs/php-enum with added singletons
+ * to be able use strict equals.
+ *
+ * Examples:
+ *
+ * final class Hash extends Enum
+ * {
+ *   const MD5 = 'md5';
+ *   const SHA1 = 'sha1';
+ * }
+ *
+ * $a = Hash::MD5();
+ * var_dump($a === Hash::MD5());
+ * > true
+ *
+ * // ALWAYS use strict equal! see the problem
+ * var_dump($a == Hash::SHA1());
+ * > true
+ *
+ * var_dump($a->getValue() === Hash::MD5);
+ * > true
+ *
+ * function crack(Hash $hash) {
+ *   echo 'cracking ... ' . $hash;
+ * }
+ *
+ * crack(Hash::SHA1());
+ * > cracking ... sha1
+ * crack(Hash::SHA1);
+ * > throws TypeError
+ *
+ * switch ($a->getValue()) {
+ *   case Hash::MD5: ...
+ *   case Hash::SHA1: ...
+ * }
+ *
+ * @author Ondrej Esler <ondrej.esler@intraworlds.com>
+ */
+abstract class Enum
+{
+    /** @var string */
+    private $key;
+
+    /** @var mixed */
+    private $_value;
+
+    /** @var array */
+    private static $_singletons = [];
+
+    /**
+     * Constructor
+     *
+     * @param string $key
+     */
+    final private function __construct(string $key) {
+        if (!defined(static::class . '::' . $key)) {
+            throw new \InvalidArgumentException('Unknown constant: ' . static::class . '::' . $key);
+        }
+
+        $this->key   = $key;
+        $this->value = \constant(static::class . '::' . $key);
+    }
+
+    /**
+     * Map class constants to static methods const FOO => FOO(), returns singleton of an enum with value of constant
+     *
+     * @param string $key
+     * @param array  $arguments
+     *
+     * @return Enum
+     */
+    final public static function __callStatic(string $key, array $arguments): Enum {
+        $singletonId = static::class . $key;
+
+        if (empty(self::$_singletons[$singletonId])) {
+            self::$_singletons[$singletonId] = new static($key);
+        }
+
+        return self::$_singletons[$singletonId];
+    }
+
+    /**
+     * Returns string representation of constant value
+     *
+     * @return string
+     */
+    final public function __toString(): string {
+        return is_array($this->value) ? json_encode($this->value) : (string) $this->value;
+    }
+
+    /**
+     * Return TRUE if given enum is the same, FALSE otherwise
+     *
+     * @param Enum $enum
+     *
+     * @return bool
+     */
+    final public function equals(Enum $enum): bool {
+        return $this === $enum;
+    }
+
+    /**
+     * Returns name of constant
+     *
+     * @return string
+     */
+    final public function getKey(): string {
+        return $this->key;
+    }
+
+    /**
+     * Returns value of constant
+     *
+     * @return mixed
+     */
+    final public function getValue() {
+        return $this->value;
+    }
+
+    /**
+     * Returns list of names of constants
+     *
+     * @return string[]
+     */
+    final public static function keys(): array {
+        return array_keys(static::toArray());
+    }
+
+    /**
+     * Returns list of values of constants
+     *
+     * @return mixed[]
+     */
+    final public static function values(): array {
+        return array_values(static::toArray());
+    }
+
+    /**
+     * Returns array with all constants eg. [key => value, ...]
+     *
+     * @return mixed[]
+     */
+    final public static function toArray(): array {
+        return (new \ReflectionClass(static::class))->getConstants();
+    }
+
+}
diff --git a/tests/EnumTest.php b/tests/EnumTest.php
new file mode 100644
index 0000000..7938531
--- /dev/null
+++ b/tests/EnumTest.php
@@ -0,0 +1,79 @@
+<?php declare(strict_types=1);
+
+namespace IW;
+
+use PHPUnit\Framework\TestCase;
+
+class EnumTest extends TestCase
+{
+
+    function testFailWhenInvalidKey() {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Unknown constant: IW\IntraWorldsEnum::KIEV');
+        IntraWorldsEnum::KIEV();
+    }
+
+    function testMethodEquals() {
+        $city = IntraWorldsEnum::PILSEN();
+
+        $this->assertTrue($city->equals(IntraWorldsEnum::PILSEN()));
+        $this->assertTrue(IntraWorldsEnum::PILSEN()->equals($city));
+
+        $this->assertFalse($city->equals(IntraWorldsEnum::NEW_YORK()));
+        $this->assertFalse(IntraWorldsEnum::TAMPA()->equals($city));
+    }
+
+    function testThatTwoInstancesAreTheSame() {
+        $this->assertSame(IntraWorldsEnum::TAMPA(), IntraWorldsEnum::TAMPA());
+    }
+
+    function testMethodToString() {
+        $this->assertSame('1', (string) IntraWorldsEnum::PILSEN());
+        $this->assertSame('0.33333333333333', (string) IntraWorldsEnum::TAMPA());
+        $this->assertSame('{"foo":["bar"]}', (string) IntraWorldsEnum::MUNICH());
+    }
+
+    function testMethodGetValue() {
+        $this->assertSame(true, IntraWorldsEnum::PILSEN()->getValue());
+        $this->assertSame(['foo' => ['bar']], IntraWorldsEnum::MUNICH()->getValue());
+        $this->assertSame(42, IntraWorldsEnum::NEW_YORK()->getValue());
+        $this->assertSame(1 / 3, IntraWorldsEnum::TAMPA()->getValue());
+    }
+
+    function testMethodGetKey() {
+        $this->assertSame('PILSEN', IntraWorldsEnum::PILSEN()->getKey());
+        $this->assertSame('MUNICH', IntraWorldsEnum::MUNICH()->getKey());
+        $this->assertSame('NEW_YORK', IntraWorldsEnum::NEW_YORK()->getKey());
+        $this->assertSame('TAMPA', IntraWorldsEnum::TAMPA()->getKey());
+    }
+
+    function testMethodKeys() {
+        $this->assertSame(['PILSEN', 'MUNICH', 'NEW_YORK', 'TAMPA'], IntraWorldsEnum::keys());
+    }
+
+    function testMethodValues() {
+        $this->assertSame([true, ['foo' => ['bar']], 42, 1 / 3], IntraWorldsEnum::values());
+    }
+
+    function testMethodToArray() {
+        $this->assertSame([
+            'PILSEN' => true,
+            'MUNICH' => ['foo' => ['bar']],
+            'NEW_YORK' => 42,
+            'TAMPA' => 1 / 3,
+        ], IntraWorldsEnum::toArray());
+    }
+}
+
+/**
+ * A value object representing testing enum
+ *
+ * @author Ondrej Esler <ondrej.esler@intraworlds.com>
+ */
+class IntraWorldsEnum extends Enum
+{
+    const PILSEN   = true;
+    const MUNICH   = ['foo' => ['bar']];
+    const NEW_YORK = 42;
+    const TAMPA    = 1 / 3;
+}