Why Does PHP Throw 'Strict Standards: Declaration of childClass::customMethod() Should Be Compatible with that of parentClass::customMethod()'?

Compatibility in PHP Method Declarations

In PHP, the error "Strict Standards: Declaration of childClass::customMethod() should be compatible with that of parentClass::customMethod()" indicates a discrepancy between the declaration of a method in a child class and its parent method.

Possible Causes:

The error occurs when the child method has either:

• Different arguments: The number, order, or data types of the method's arguments should match that of the parent method.
• Different access level: The access level (public, private, or protected) of the child method must be the same as or less restrictive than that of the parent method.

Finding Compatibility Information:

PHP uses the following rules to define method compatibility:

• Arguments: Argument declarations must match both in number and type.
• Access level: Child method access can be more restrictive (e.g., public to private) but not less restrictive (e.g., private to public).
• Return types: Child method return type can be covariant, meaning it can return a subclass of the parent return type.

Additional documentation and examples on method compatibility can be found in the following PHP Manual pages:

• [Overloading and Inheritance](https://www.php.net/manual/en/language.oop5.overloading.php)
• [Method Visibility](https://www.php.net/manual/en/language.oop5.visibility.php)
• [Covariance and Contravariance](https://www.php.net/manual/en/language.oop5.variance.php)

The above is the detailed content of Why Does PHP Throw 'Strict Standards: Declaration of childClass::customMethod() Should Be Compatible with that of parentClass::customMethod()'?. For more information, please follow other related articles on the PHP Chinese website!