How to Ensure Method Compatibility Between PHP Parent and Child Classes?

PHP: Ensuring Method Compatibility Between Parent and Child Classes

When extending a parent class in PHP, it is essential to ensure compatibility between the inherited methods and their overrides in the child class. Ignoring this compatibility may lead to the following error:

Strict Standards: Declaration of childClass::customMethod() should be compatible with that of parentClass::customMethod()

Root Causes of the Compatibility Issue

The error arises when the overridden method (childClass::customMethod()) differs from the parent method (parentClass::customMethod()) in any of the following ways:

• Different Argument List: The number or data types of the method parameters must match.
• Differing Access Level: The overridden method must have the same or a more relaxed access level (e.g., public can override protected but not vice versa).

Interpreting Compatibility

In PHP, the compatibility requirement means that the child class method must not modify the following aspects of the parent method:

• Return type
• Argument list (number and types)
• Access level
• Static or final modifiers

Additional Documentation

For further insights on method compatibility, refer to the official PHP documentation:

• [PHP: Method Overloading](https://www.php.net/manual/en/language.oop5.overloading.php)
• [PHP: Method Compatibility](https://www.php.net/manual/en/language.oop5.basic.php#language.oop5.basic.class.inherited)

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