Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Component/Uuid/Com.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Uuid\Com.
+ */
+
+namespace Drupal\Component\Uuid;
+
+/**
+ * UUID implementation using the Windows internal GUID extension.
+ *
+ * @see http://php.net/com_create_guid
+ */
+class Com implements UuidInterface {
+  /**
+   * {@inheritdoc}
+   */
+  public function generate() {
+    // Remove {} wrapper and make lower case to keep result consistent.
+    return strtolower(trim(com_create_guid(), '{}'));
+  }
+}

core/lib/Drupal/Component/Uuid/Pecl.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Uuid\Pecl.
+ */
+
+namespace Drupal\Component\Uuid;
+
+/**
+ * UUID implementation using the PECL extension.
+ */
+class Pecl implements UuidInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function generate() {
+    return uuid_create(UUID_TYPE_DEFAULT);
+  }
+}

core/lib/Drupal/Component/Uuid/Php.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Uuid\Php.
+ */
+
+namespace Drupal\Component\Uuid;
+
+use Drupal\Component\Utility\Crypt;
+
+/**
+ * Generates a UUID v4 using PHP code.
+ *
+ * Loosely based on Ruby's UUIDTools generate_random logic.
+ *
+ * @see http://uuidtools.rubyforge.org/api/classes/UUIDTools/UUID.html
+ */
+class Php implements UuidInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function generate() {
+    $hex = substr(hash('sha256', Crypt::randomBytes(16)), 0, 32);
+
+    // The field names refer to RFC 4122 section 4.1.2.
+    $time_low = substr($hex, 0, 8);
+    $time_mid = substr($hex, 8, 4);
+
+    $time_hi_and_version = base_convert(substr($hex, 12, 4), 16, 10);
+    $time_hi_and_version &= 0x0FFF;
+    $time_hi_and_version |= (4 << 12);
+
+    $clock_seq_hi_and_reserved = base_convert(substr($hex, 16, 4), 16, 10);
+    $clock_seq_hi_and_reserved &= 0x3F;
+    $clock_seq_hi_and_reserved |= 0x80;
+
+    $clock_seq_low = substr($hex, 20, 2);
+    $nodes = substr($hex, 20);
+
+    $uuid = sprintf('%s-%s-%04x-%02x%02x-%s',
+      $time_low, $time_mid,
+      $time_hi_and_version, $clock_seq_hi_and_reserved,
+      $clock_seq_low, $nodes);
+
+    return $uuid;
+  }
+
+}

core/lib/Drupal/Component/Uuid/Uuid.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Uuid\Uuid.
+ */
+
+namespace Drupal\Component\Uuid;
+
+/**
+ * UUID Helper methods.
+ */
+class Uuid {
+
+  /**
+   * The pattern used to validate a UUID string.
+   */
+  const VALID_PATTERN = '[0-9a-f]{8}-([0-9a-f]{4}-){3}[0-9a-f]{12}';
+
+  /**
+   * Checks that a string appears to be in the format of a UUID.
+   *
+   * Implementations should not implement validation, since UUIDs should be in
+   * a consistent format across all implementations.
+   *
+   * @param string $uuid
+   *   The string to test.
+   *
+   * @return bool
+   *   TRUE if the string is well formed, FALSE otherwise.
+   */
+  public static function isValid($uuid) {
+    return (bool) preg_match('/^' . self::VALID_PATTERN . '$/', $uuid);
+  }
+
+}

core/lib/Drupal/Component/Uuid/UuidInterface.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Uuid\UuidInterface.
+ */
+
+namespace Drupal\Component\Uuid;
+
+/**
+ * Interface that defines a UUID backend.
+ */
+interface UuidInterface {
+
+  /**
+   * Generates a Universally Unique IDentifier (UUID).
+   *
+   * @return
+   *   A 16 byte integer represented as a hex string formatted with 4 hyphens.
+   */
+  public function generate();
+}