diff --git a/README.md b/README.md
index cfe77cc..b4e671e 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,3 @@
 # Useful PHP Basics
 
-This is a collection of generic [Classes](https://www.php.net/manual/en/language.oop5.php) and useful [Traits](https://www.php.net/manual/en/language.oop5.traits.php) for your PHP projects.
+This is a collection of generic [Classes](https://www.php.net/manual/en/language.oop5.php), [Functions](https://www.php.net/manual/en/language.functions.php) and useful [Traits](https://www.php.net/manual/en/language.oop5.traits.php) for your PHP projects.
diff --git a/composer.json b/composer.json
index dbcf188..8216d2d 100644
--- a/composer.json
+++ b/composer.json
@@ -1,16 +1,19 @@
 {
     "name": "opencultureconsulting/basics",
-    "description": "This is a collection of generic Classes and useful Traits for PHP projects.",
+    "description": "This is a collection of generic Classes, Functions and useful Traits for PHP projects.",
     "type": "library",
     "keywords": [
-        "trait",
-        "getter",
-        "setter",
-        "singleton",
-        "list",
-        "queue",
-        "stack",
-        "errorhandler"
+        "ArrayAccess",
+        "Countable",
+        "Getter",
+        "Iterator",
+        "IteratorAggregate",
+        "Setter",
+        "Singleton",
+        "StrictList",
+        "StrictQueue",
+        "StrictStack",
+        "throwErrorException"
     ],
     "homepage": "https://github.com/opencultureconsulting/php-basics",
     "readme": "README.md",
diff --git a/src/Traits/ArrayAccess.php b/src/Traits/ArrayAccess.php
new file mode 100644
index 0000000..7f0c376
--- /dev/null
+++ b/src/Traits/ArrayAccess.php
@@ -0,0 +1,96 @@
+<?php
+
+/**
+ * Useful PHP Basics
+ * Copyright (C) 2023 Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace OCC\Basics\Traits;
+
+/**
+ * A generic implementation of the ArrayAccess interface.
+ *
+ * @author Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ * @package opencultureconsulting/basics
+ *
+ * @implements \ArrayAccess
+ */
+trait ArrayAccess /* implements \ArrayAccess */
+{
+    /**
+     * Holds the array-accessible data.
+     */
+    private array $data = [];
+
+    /**
+     * Whether the specified offset exists.
+     * @see \ArrayAccess::offsetExists()
+     *
+     * @param mixed $offset The offset to check for
+     *
+     * @return bool Whether the offset exists
+     */
+    public function offsetExists(mixed $offset): bool
+    {
+        return isset($this->data[$offset]);
+    }
+
+    /**
+     * Retrieve data at the specified offset.
+     * @see \ArrayAccess::offsetGet()
+     *
+     * @param mixed $offset The offset to retrieve at
+     *
+     * @return mixed The value at the offset or NULL
+     */
+    public function offsetGet(mixed $offset): mixed
+    {
+        return $this->data[$offset] ?? null;
+    }
+
+    /**
+     * Assign a value to the specified offset.
+     * @see \ArrayAccess::offsetSet()
+     *
+     * @param mixed $offset The offset to assign to or NULL to append
+     * @param mixed $value The value to set
+     *
+     * @return void
+     */
+    public function offsetSet(mixed $offset, mixed $value): void
+    {
+        if (is_null($offset)) {
+            $this->data[] = $value;
+        } else {
+            $this->data[$offset] = $value;
+        }
+    }
+
+    /**
+     * Unset the specified offset.
+     * @see \ArrayAccess::offsetUnset()
+     *
+     * @param mixed $offset The offset to unset
+     *
+     * @return void
+     */
+    public function offsetUnset(mixed $offset): void
+    {
+        unset($this->data[$offset]);
+    }
+}
diff --git a/src/Traits/Countable.php b/src/Traits/Countable.php
new file mode 100644
index 0000000..4c8ed99
--- /dev/null
+++ b/src/Traits/Countable.php
@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * Useful PHP Basics
+ * Copyright (C) 2023 Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace OCC\Basics\Traits;
+
+/**
+ * A generic implementation of the Countable interface.
+ *
+ * @author Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ * @package opencultureconsulting/basics
+ *
+ * @implements \Countable
+ */
+trait Countable /* implements \Countable */
+{
+    /**
+     * Holds the countable data.
+     */
+    private array $data = [];
+
+    /**
+     * Count the data items.
+     * @see \Countable::count()
+     *
+     * @return int The number of data items
+     */
+    public function count(): int
+    {
+        return count($this->data);
+    }
+}
diff --git a/src/Traits/Iterator.php b/src/Traits/Iterator.php
new file mode 100644
index 0000000..443f696
--- /dev/null
+++ b/src/Traits/Iterator.php
@@ -0,0 +1,94 @@
+<?php
+
+/**
+ * Useful PHP Basics
+ * Copyright (C) 2023 Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace OCC\Basics\Traits;
+
+/**
+ * A generic implementation of the Iterator interface.
+ *
+ * @author Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ * @package opencultureconsulting/basics
+ *
+ * @implements \Iterator
+ */
+trait Iterator /* implements \Iterator */
+{
+    /**
+     * Holds the iterable data.
+     */
+    private array $data = [];
+
+    /**
+     * Return the current item.
+     * @see \Iterator::current()
+     *
+     * @return mixed The current item or FALSE if invalid
+     */
+    public function current(): mixed
+    {
+        return current($this->data);
+    }
+
+    /**
+     * Return the current key.
+     * @see \Iterator::key()
+     *
+     * @return mixed The current key or NULL if invalid
+     */
+    public function key(): mixed
+    {
+        return key($this->data);
+    }
+
+    /**
+     * Move forward to next item.
+     * @see \Iterator::next()
+     *
+     * @return void
+     */
+    public function next(): void
+    {
+        next($this->data);
+    }
+
+    /**
+     * Rewind the iterator to the first item.
+     * @see \Iterator::rewind()
+     *
+     * @return void
+     */
+    public function rewind(): void
+    {
+        reset($this->data);
+    }
+
+    /**
+     * Checks if current position is valid.
+     * @see \Iterator::valid()
+     *
+     * @return bool Whether the current position is valid
+     */
+    public function valid(): bool
+    {
+        return !is_null($this->key());
+    }
+}
diff --git a/src/Traits/IteratorAggregate.php b/src/Traits/IteratorAggregate.php
new file mode 100644
index 0000000..e8a96bc
--- /dev/null
+++ b/src/Traits/IteratorAggregate.php
@@ -0,0 +1,52 @@
+<?php
+
+/**
+ * Useful PHP Basics
+ * Copyright (C) 2023 Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace OCC\Basics\Traits;
+
+use ArrayIterator;
+
+/**
+ * A generic implementation of the IteratorAggregate interface.
+ *
+ * @author Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>
+ * @package opencultureconsulting/basics
+ *
+ * @implements \IteratorAggregate
+ */
+trait IteratorAggregate /* implements \IteratorAggregate */
+{
+    /**
+     * Holds the iterable data.
+     */
+    private array $data = [];
+
+    /**
+     * Retrieve an external iterator.
+     * @see \IteratorAggregate::getIterator()
+     *
+     * @return \ArrayIterator
+     */
+    public function getIterator(): ArrayIterator
+    {
+        return new ArrayIterator($this->data);
+    }
+}