How to make a deep copy or clone of an object in PHP?
Sep 21, 2025 am 12:30 AM
Use unserialize(serialize($obj)) for deep copying when all data is serializable; otherwise, implement __clone() to manually duplicate nested objects and avoid shared references.
Copying an object in PHP can be tricky because the default assignment creates a shallow copy, meaning changes to nested objects or arrays affect the original. To avoid this, you need a deep copy—where all levels of data are duplicated independently.
Understanding Shallow vs Deep Copy
When you use the assignment operator (=) or clone without extra handling, PHP performs a shallow copy:
? Properties that are objects or arrays still reference the original.? Modifying nested data in the copy affects the original object.
? A true deep copy duplicates everything recursively.
Using Unserialize and Serialize for Deep Copy
The most common and effective way to achieve a deep copy is by serializing the object to a string and then unserializing it back:
$deepCopy = unserialize(serialize($originalObject));This method works because:
? serialize() converts the entire object structure into a string, including nested objects.? unserialize() reconstructs a completely new instance from that string.
? No references to the original object remain.
Note: This only works if the object and all its nested properties are serializable (i.e., no closures or resource types).
Implementing __clone() for Custom Deep Cloning
If you need more control or your object contains non-serializable data, override the __clone() magic method:
class MyClass {????public $data;
????public function __clone() {
????????$this->data = unserialize(serialize($this->data)); // deep copy nested structure
????}
}
$copy = clone $original;
In __clone(), manually clone any property that should not be shared, such as child objects or complex arrays.
Limitations and Considerations
Be aware of these caveats:
? serialize/unserialize fails with closures (anonymous functions) or resources like database connections.? Performance overhead with large or deeply nested objects.
? Objects must implement Serializable or avoid restricted types for serialization to work.
For objects with callbacks or external dependencies, custom cloning via __clone() is safer and more predictable.
Basically, use unserialize(serialize()) for simple cases where full serialization is safe. For complex objects, rely on properly implemented __clone() methods to manage nested data. It’s not hard once you know which approach fits your object structure.
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