diff --git a/src/ArrayClasses/ArrayClass.php b/src/ArrayClasses/ArrayClass.php
index a32b610..88b3ef5 100644
--- a/src/ArrayClasses/ArrayClass.php
+++ b/src/ArrayClasses/ArrayClass.php
@@ -2,60 +2,16 @@
 
 namespace jrosset\ArrayClasses;
 
-use OutOfRangeException;
-
 /**
  * An array
  */
-class ArrayClass extends ImmutableArrayClass {
-    /**
-     * Set or replace a cell value
-     *
-     * @param mixed $offset The cell offset
-     * @param mixed $value  The cell new value
-     *
-     * @return $this
-     */
-    public function set ($offset, $value): self {
-        $this->array[$offset] = $value;
-        return $this;
-    }
-    /**
-     * Remove a cell
-     *
-     * @param mixed     $offset                      The cell offset
-     * @param bool|null $throwsForNonExistentElement If set, temporarily override {@see ImmutableArrayClass::$throwsForNonExistentElement}
-     *
-     * @return $this
-     */
-    public function del ($offset, ?bool $throwsForNonExistentElement = null): self {
-        if ($throwsForNonExistentElement ?? $this->throwsForNonExistentElement() && !$this->has($offset)) {
-            throw new OutOfRangeException();
-        }
-        unset($this->array[$offset]);
-
-        return $this;
-    }
+class ArrayClass extends ImmutableArrayClass implements IArrayClass {
+    use TInternalArray;
 
-    /**
-     * Create an immutable copy
-     *
-     * @return ImmutableArrayClass The immutable copy
-     */
-    public function toImmutableArrayClass (): ImmutableArrayClass {
-        return new ImmutableArrayClass($this);
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function offsetSet ($offset, $value): void {
-        $this->set($offset, $value);
-    }
     /**
      * @inheritDoc
      */
-    public function offsetUnset ($offset): void {
-        $this->del($offset);
+    public function toImmutable (): IImmutableArrayClass {
+        return new ImmutableArrayClass($this->array, $this->throwsForNonExistentElement());
     }
 }
\ No newline at end of file
diff --git a/src/ArrayClasses/IArrayClass.php b/src/ArrayClasses/IArrayClass.php
new file mode 100644
index 0000000..4971443
--- /dev/null
+++ b/src/ArrayClasses/IArrayClass.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace jrosset\ArrayClasses;
+
+interface IArrayClass extends IImmutableArrayClass {
+    /**
+     * Create or replace a cell
+     *
+     * @param mixed $cellName  The cell name/offset
+     * @param mixed $cellValue The cell new value
+     *
+     * @return $this
+     */
+    public function set ($cellName, $cellValue): self;
+    /**
+     * Remove a cell
+     *
+     * @param mixed $cellName The cell name/offset
+     *
+     * @return $this
+     */
+    public function del ($cellName): self;
+
+    /**
+     * Create an immutable copy
+     *
+     * @return IImmutableArrayClass The immutable copy
+     */
+    public function toImmutable (): IImmutableArrayClass;
+}
\ No newline at end of file
diff --git a/src/ArrayClasses/IImmutableArrayClass.php b/src/ArrayClasses/IImmutableArrayClass.php
new file mode 100644
index 0000000..3c7fb1e
--- /dev/null
+++ b/src/ArrayClasses/IImmutableArrayClass.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace jrosset\ArrayClasses;
+
+use ArrayAccess;
+use Countable;
+use IteratorAggregate;
+use JsonSerializable;
+use Serializable;
+
+interface IImmutableArrayClass extends IteratorAggregate, JsonSerializable, Serializable, Countable, ArrayAccess, IArrayCast {
+    /**
+     * Check if a cell exists
+     *
+     * @param mixed $cellName The cell name/offset
+     *
+     * @return bool Is the cell exists ?
+     */
+    public function has ($cellName): bool;
+    /**
+     * Get the value of a cell
+     *
+     * @param mixed $cellName The cell name/offset
+     *
+     * @return mixed The cell value
+     */
+    public function get ($cellName);
+
+    /**
+     * Create a mutable copy
+     *
+     * @return IArrayClass The mutable copy
+     */
+    public function toMutable (): IArrayClass;
+}
\ No newline at end of file
diff --git a/src/ArrayClasses/ImmutableArrayClass.php b/src/ArrayClasses/ImmutableArrayClass.php
index 27ab345..31b7039 100644
--- a/src/ArrayClasses/ImmutableArrayClass.php
+++ b/src/ArrayClasses/ImmutableArrayClass.php
@@ -2,193 +2,16 @@
 
 namespace jrosset\ArrayClasses;
 
-use ArrayAccess;
-use ArrayIterator;
-use Countable;
-use InvalidArgumentException;
-use IteratorAggregate;
-use JsonSerializable;
-use OutOfRangeException;
-use Serializable;
-use Traversable;
-
 /**
  * An immutable array
  */
-class ImmutableArrayClass implements IteratorAggregate, JsonSerializable, Serializable, Countable, ArrayAccess, IArrayCast {
-    /**
-     * @var array The internal array
-     */
-    protected array $array;
-    /**
-     * @var bool Throws an exception for nonexistent elements ?
-     */
-    private bool $throwsForNonExistentElement;
-
-    /**
-     * Initialize the array
-     *
-     * @param IArrayCast|array|null $initial                     The initial value
-     * @param bool                  $throwsForNonExistentElement Throws an exception for nonexistent elements ?
-     */
-    public function __construct ($initial = null, bool $throwsForNonExistentElement = true) {
-        $this->setThrowsForNonExistentElement($throwsForNonExistentElement);
-
-        if (is_array($initial)) {
-            $this->array = $initial;
-        }
-        elseif (is_null($initial)) {
-            $this->array = [];
-        }
-        elseif ($initial instanceof IArrayCast) {
-            $this->array = $initial->toArray();
-        }
-        else {
-            throw new InvalidArgumentException('The initial value is not valid: null, array or ' . IArrayCast::class);
-        }
-    }
-    /**
-     * Get the value of a cell
-     *
-     * @param mixed $offset The cell offset
-     *
-     * @return mixed|null The cell value
-     */
-    public function __invoke ($offset) {
-        return $this->get($offset);
-    }
-    /**
-     * Set information to dump
-     *
-     * @return array The information to dump
-     *
-     * @see https://www.php.net/manual/function.var-dump.php
-     */
-    public function __debugInfo (): array {
-        return [
-            'array' => $this->array,
-        ];
-    }
-
-    /**
-     * Check if a cell offset exists
-     *
-     * @param mixed $offset The cell offset
-     *
-     * @return bool True if the cell offset exists
-     */
-    public function has ($offset): bool {
-        return array_key_exists($offset, $this->array);
-    }
-    /**
-     * Get the value of a cell
-     *
-     * @param mixed     $offset                      The cell offset
-     * @param bool|null $throwsForNonExistentElement If set, temporarily override {@see ImmutableArrayClass::$throwsForNonExistentElement}
-     *
-     * @return mixed|null The cell value
-     */
-    public function get ($offset, ?bool $throwsForNonExistentElement = null) {
-        if ($this->has($offset)) {
-            return $this->array[$offset];
-        }
-        if ($throwsForNonExistentElement ?? $this->throwsForNonExistentElement()) {
-            throw new OutOfRangeException();
-        }
-        return null;
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function toArray (): array {
-        return $this->array;
-    }
-    /**
-     * Create a mutable copy
-     *
-     * @return ArrayClass The mutable copy
-     */
-    public function toMutableArrayClass (): ArrayClass {
-        return new ArrayClass($this);
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function count (): int {
-        return count($this->array);
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function getIterator (): Traversable {
-        return new ArrayIterator($this->array);
-    }
+class ImmutableArrayClass implements IImmutableArrayClass {
+    use TImmutableInternalArray;
 
     /**
      * @inheritDoc
      */
-    public function offsetExists ($offset): bool {
-        return $this->has($offset);
-    }
-    /**
-     * @inheritDoc
-     */
-    public function offsetGet ($offset) {
-        return $this->get($offset);
-    }
-    /**
-     * @inheritDoc
-     */
-    public function offsetSet ($offset, $value): void {
-        throw new ImmutableException();
-    }
-    /**
-     * @inheritDoc
-     */
-    public function offsetUnset ($offset): void {
-        throw new ImmutableException();
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function serialize (): string {
-        return serialize($this->array);
-    }
-    /**
-     * @inheritDoc
-     */
-    public function unserialize ($data): void {
-        $this->array = unserialize($data);
-    }
-
-    /**
-     * @inheritDoc
-     */
-    public function jsonSerialize () {
-        return $this->array;
-    }
-
-    /**
-     * Throws an exception for nonexistent elements ?
-     *
-     * @return bool Throws an exception for nonexistent elements ?
-     */
-    public function throwsForNonExistentElement (): bool {
-        return $this->throwsForNonExistentElement;
-    }
-    /**
-     * Set if throws an exception for nonexistent elements
-     *
-     * @param bool $throwsForNonExistentElement Throws an exception for nonexistent elements ?
-     *
-     * @return $this
-     */
-    public function setThrowsForNonExistentElement (bool $throwsForNonExistentElement): self {
-        $this->throwsForNonExistentElement = $throwsForNonExistentElement;
-        return $this;
+    public function toMutable (): IArrayClass {
+        return new ArrayClass($this->array, $this->throwsForNonExistentElement());
     }
 }
\ No newline at end of file
diff --git a/src/ArrayClasses/TImmutableInternalArray.php b/src/ArrayClasses/TImmutableInternalArray.php
new file mode 100644
index 0000000..0ec0e8d
--- /dev/null
+++ b/src/ArrayClasses/TImmutableInternalArray.php
@@ -0,0 +1,168 @@
+<?php
+
+namespace jrosset\ArrayClasses;
+
+use ArrayIterator;
+use InvalidArgumentException;
+use OutOfRangeException;
+use Traversable;
+
+trait TImmutableInternalArray {
+    /**
+     * @var array The internal array
+     */
+    protected array $array = [];
+    /**
+     * @var bool Throws an exception for nonexistent elements ?
+     */
+    private bool $throwsForNonExistentElement = true;
+
+    /**
+     * Initialize the array
+     *
+     * @param IArrayCast|array|null $initial                     The initial value
+     * @param bool                  $throwsForNonExistentElement Throws an exception for nonexistent elements ?
+     */
+    public function __construct ($initial = null, bool $throwsForNonExistentElement = true) {
+        $this->setThrowsForNonExistentElement($throwsForNonExistentElement);
+
+        if (is_array($initial)) {
+            $this->array = $initial;
+        }
+        elseif (is_null($initial)) {
+            $this->array = [];
+        }
+        elseif ($initial instanceof IArrayCast) {
+            $this->array = $initial->toArray();
+        }
+        else {
+            throw new InvalidArgumentException('The initial value is not valid: null, array or ' . IArrayCast::class);
+        }
+    }
+    /**
+     * Set information to dump
+     *
+     * @return array The information to dump
+     *
+     * @see https://www.php.net/manual/function.var-dump.php
+     */
+    public function __debugInfo (): array {
+        return [
+            'array' => $this->array,
+        ];
+    }
+
+    /**
+     * Check if a cell offset exists
+     *
+     * @param mixed $offset The cell offset
+     *
+     * @return bool True if the cell offset exists
+     */
+    public function has ($offset): bool {
+        return array_key_exists($offset, $this->array);
+    }
+    /**
+     * Get the value of a cell
+     *
+     * @param mixed     $offset                      The cell offset
+     * @param bool|null $throwsForNonExistentElement If set, temporarily override {@see ImmutableArrayClass::$throwsForNonExistentElement}
+     *
+     * @return mixed|null The cell value
+     */
+    public function get ($offset, ?bool $throwsForNonExistentElement = null) {
+        if ($this->has($offset)) {
+            return $this->array[$offset];
+        }
+        if ($throwsForNonExistentElement ?? $this->throwsForNonExistentElement()) {
+            throw new OutOfRangeException();
+        }
+        return null;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function toArray (): array {
+        return $this->array;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function count (): int {
+        return count($this->array);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getIterator (): Traversable {
+        return new ArrayIterator($this->array);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function offsetExists ($offset): bool {
+        return $this->has($offset);
+    }
+    /**
+     * @inheritDoc
+     */
+    public function offsetGet ($offset) {
+        return $this->get($offset);
+    }
+    /**
+     * @inheritDoc
+     */
+    public function offsetSet ($offset, $value): void {
+        throw new ImmutableException();
+    }
+    /**
+     * @inheritDoc
+     */
+    public function offsetUnset ($offset): void {
+        throw new ImmutableException();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function serialize (): string {
+        return serialize($this->array);
+    }
+    /**
+     * @inheritDoc
+     */
+    public function unserialize ($data): void {
+        $this->array = unserialize($data);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function jsonSerialize () {
+        return $this->array;
+    }
+
+    /**
+     * Throws an exception for nonexistent elements ?
+     *
+     * @return bool Throws an exception for nonexistent elements ?
+     */
+    public function throwsForNonExistentElement (): bool {
+        return $this->throwsForNonExistentElement;
+    }
+    /**
+     * Set if throws an exception for nonexistent elements
+     *
+     * @param bool $throwsForNonExistentElement Throws an exception for nonexistent elements ?
+     *
+     * @return $this
+     */
+    public function setThrowsForNonExistentElement (bool $throwsForNonExistentElement): self {
+        $this->throwsForNonExistentElement = $throwsForNonExistentElement;
+        return $this;
+    }
+}
\ No newline at end of file
diff --git a/src/ArrayClasses/TInternalArray.php b/src/ArrayClasses/TInternalArray.php
new file mode 100644
index 0000000..e9ba1d0
--- /dev/null
+++ b/src/ArrayClasses/TInternalArray.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace jrosset\ArrayClasses;
+
+use OutOfRangeException;
+
+trait TInternalArray {
+    /**
+     * Set or replace a cell value
+     *
+     * @param mixed $offset The cell offset
+     * @param mixed $value  The cell new value
+     *
+     * @return $this
+     */
+    public function set ($offset, $value): self {
+        $this->array[$offset] = $value;
+        return $this;
+    }
+    /**
+     * Remove a cell
+     *
+     * @param mixed     $offset                      The cell offset
+     * @param bool|null $throwsForNonExistentElement If set, temporarily override {@see ImmutableArrayClass::$throwsForNonExistentElement}
+     *
+     * @return $this
+     */
+    public function del ($offset, ?bool $throwsForNonExistentElement = null): self {
+        if ($throwsForNonExistentElement ?? $this->throwsForNonExistentElement() && !$this->has($offset)) {
+            throw new OutOfRangeException();
+        }
+        unset($this->array[$offset]);
+
+        return $this;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function offsetSet ($offset, $value): void {
+        $this->set($offset, $value);
+    }
+    /**
+     * @inheritDoc
+     */
+    public function offsetUnset ($offset): void {
+        $this->del($offset);
+    }
+}
\ No newline at end of file