Declaration of Methods should be Compatible with Parent Methods in PHP

Question

Strict Standards  Declaration of childClass  customMethod   should be compatible with that of parentClass  customMethod     What are possible causes of this error in PHP  Where can I find information about what it means to be compatible

User · Answer

This message means that there are certain possible method calls which may fail at run-time. Suppose you have

class A { public function foo($a = 1) {;}}
class B extends A { public function foo($a) {;}}
function bar(A $a) {$a->foo();}

The compiler only checks the call $a->foo() against the requirements of A::foo() which requires no parameters. $a may however be an object of class B which requires a parameter and so the call would fail at runtime.

This however can never fail and does not trigger the error

class A { public function foo($a) {;}}
class B extends A { public function foo($a = 1) {;}}
function bar(A $a) {$a->foo();}

So no method may have more required parameters than its parent method.

The same message is also generated when type hints do not match, but in this case PHP is even more restrictive. This gives an error:

class A { public function foo(StdClass $a) {;}}
class B extends A { public function foo($a) {;}}

as does this:

class A { public function foo($a) {;}}
class B extends A { public function foo(StdClass $a) {;}}

That seems more restrictive than it needs to be and I assume is due to internals.

Visibility differences cause a different error, but for the same basic reason. No method can be less visible than its parent method.

User · Answer

if you wanna keep OOP form without turning any error off  you can also   class A       public function foo                       class B extends A         instead of        public function foo  a   b   c          public function foo             list  a   b   c    func get args

User · Answer

I faced this problem while trying to extend an existing class from GitHub  I m gonna try to explain myself  first writing the class as I though it should be  and then the class as it is now   What I though  namespace mycompany CutreApi   use mycompany CutreApi ClassOfVendor   class CutreApi extends  vendor AwesomeApi AwesomeApi      public function whatever    ClassOfVendor              return new ClassOfVendor             What I ve finally done  namespace mycompany CutreApi   use  vendor AwesomeApi ClassOfVendor   class CutreApi extends  vendor AwesomeApi AwesomeApi      public function whatever    ClassOfVendor              return new  mycompany CutreApi ClassOfVendor             So seems that this errror raises also when you re using a method that return a namespaced class  and you try to return the same class but with other namespace  Fortunately I have found this solution  but I do not fully understand the benefit of this feature in php 7 2  for me it is normal to rewrite existing class methods as you need them  including the redefinition of input parameters and   or even behavior of the method   One downside of the previous aproach  is that IDE s could not recognise the new methods implemented in  mycompany CutreApi ClassOfVendor    So  for now  I will go with this implementation   Currently done  namespace mycompany CutreApi   use mycompany CutreApi ClassOfVendor   class CutreApi extends  vendor AwesomeApi AwesomeApi      public function getWhatever    ClassOfVendor              return new ClassOfVendor             So  instead of trying to use  whatever  method  I wrote a new one called  getWhatever   In fact both of them are doing the same  just returning a class  but with diferents namespaces as I ve described before   Hope this can help someone

User · Answer

childClass  customMethod   has different arguments  or a different access level  public private protected  than parentClass  customMethod

User · Answer

Just to expand on this error in the context of an interface  if you are type hinting your function parameters like so   interface A  use Bar   interface A       public function foo Bar  b       Class B   class B implements A       public function foo Bar  b       If you have forgotten to include the use statement on your implementing class  Class B   then you will also get this error even though the method parameters are identical

[php] Declaration of Methods should be Compatible with Parent Methods in PHP

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