<?php
 
/// parent class
interface iA {
    public function execute($str = '');
}
 
class A implements iA {
 
    public function __construct() { }
 
    public function execute($str = '')
    {
        return 'Execution ' . $str;
    }
}
 
/// child class
interface iB {
    public function execute();
}
 
class B extends A implements iB {
 
    public function __construct()
    {
        parent::__construct();
    }
 
    public function execute()
    {
        return parent::execute();
    }
 
}
 
var_dump((new B)->execute());

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