PHP Class Has Colliding Constructor Definitions Coming From Traits

Question

I have 3 files which relate one to another :

class/General.class.php
class/Database.class.php
class/User.class.php

class/General.class.php contains :

trait generalFunctions {

    private $unique_number;
    private $mysql_datetime;
    private $mysql_date;

    function __construct($unique_number, $mysql_datetime, $mysql_date) {
        $this->unique_number = $unique_number;
        $this->mysql_datetime = $mysql_datetime;
        $this->mysql_date = $mysql_date;
    }


    public function encryptData ($data) {
        $unique_number = $this->unique_number;
        $data = $unique_number . $data;
        return $data;
    }

}

class General {
    use generalFunctions;
}

?>

and class/User.class.php basically inherits from Database class :

class User extends Database {
    use generalFunctions;

    public function trialEncrypt ($data) {
    // some code here which need encryptData function from General class
    }
}

When I tried to use these classes :

<?php
include('config.php');
include('class/General.class.php');
include('class/Database.class.php');
include('class/User.class.php');

?>

I got this following error :

Fatal error: User has colliding constructor definitions coming from traits in /home/***/public_html/class/User.class.php on line 178

but when I removed use generalFunctions; from User class, then everything works fine.

Unfortunately, I can't use functions inside General class on User class.

How to solve this problem? I want to have functions inside the General class that can be used by other classes, specially class which extended from other class, such as the User class (extended from the Database class)

What is the definition of Database? Does it have a constructor? If so, that's where the collision is coming from. — jbafford, Jan 15 '16 at 04:36
Possible duplicate of [How to overload class constructor within traits in PHP >= 5.4](http://stackoverflow.com/questions/12478124/how-to-overload-class-constructor-within-traits-in-php-5-4) — Manolo, Aug 16 '16 at 13:57

score 2 · Accepted Answer · edited May 23 '17 at 12:06

Although, it's not posted here, I'm guessing that class/Database.class.php has a constructor in it as well. Since PHP doesn't really do function overloading, there can only be one constructor - you have two, the inherited one from Database and the other from generalFunctions.

What you'll need to do is alias your trait constructor function with the use statement

class User extends Database {
    use generalFunctions { 
         generalFunctions::__construct as private traitConstructor; 
    }

    public function trialEncrypt ($data) {
    // some code here which need encryptData function from General class
    }
}

Another Example: How to overload class constructor within traits in PHP >= 5.4

Also for reference: PHP Traits

You should also create a `__construct` function that calls `$this->traitConstructor()` and possibly `parent::construct()`. — Arnold Daniels, Jan 15 '16 at 05:52

score 0 · Answer 2 · answered Sep 23 '18 at 15:06

A simple code to demonstrate that the problem has been fixed in recent PHP versions:

<?php
/* The fatal error has been fixed in PHP 5.5.21 */

trait MyTrait {
    public function __construct() {}
}

class MyParent{
    public function __construct() {}
}

class MyClass1 extends MyParent{
    use MyTrait;
}

class MyClass2 extends MyParent {
    use MyTrait;
}

$o1 = new MyClass1;
$o2 = new MyClass2;

Can be viewed here: https://3v4l.org/gcp9J

PHP Class Has Colliding Constructor Definitions Coming From Traits

2 Answers2