Object in Array Giving Non-Object Message

[kebbelj]

1. In PHP 5, I used an eval statement inside a loop to dynamically construct a group of objects ...

	$evalStatement = $objName." = new ".$className."(".$fieldString.");";
	eval( $evalStatement );

2. When I echo $evalStatement, the constructors look fine ...

$Teacher_7 = new Teacher('6','Jimmy','Bond','6','Science','6','Sci','Spurs');
$Teacher_8 = new Teacher('7','Tammy','Benson','7','','3','Math','Wranglers');

3. With the object $instanceOfTeacher, I add these objects to an array which tests their "objecthood" (thanks for the code, Nogdog) ...

public function addToArrayTeacher($obj)
   {   	
      if(is_a($obj, 'Teacher'))
      {
         $this->ArrayTeacher[] = $obj;
          return(TRUE);
      }
      else
      {
         // throw exception or raise error, then:
         return(FALSE);
      }
	}

4. When I use this get_CountArray() function, I get a count of 81 (which the previous step indicates should all be objects)

	public function get_CountArray()
	{
		return count($this->ArrayTeacher);
	}

5. But when I try and access these objects by looping through ArrayTeacher...

	
     // Function Call
     $instanceOfTeacher->brand_Students( $schoolName, "Band", $corral_band ); 

 // Function Header
 public function brand_Students ( $schoolName, $subject, $theCorral )	

 // Attempt to Access Array Item containing object
 if ( $this->get_ArrayTeacher( $i )->get_subjArea() == $subject )

[B]I get this error message ...[/B]

Fatal error: Call to a member function get_subjArea() on a non-object in C:\Program Files\wamp\www\db\classes\Teacher.class.php on line 219

Anyone see what I've done wrong?

[bpat1434]

Perhaps because you need to not copy the value, but reference it:

if(is_a($obj, 'Teacher'))
      {
         $this->ArrayTeacher[] = &$obj;
          return(TRUE);
      }

Notice the & just before $obj 😉 Might not work, but it's worth a shot. Of course, you'd have to pass it by reference as well:

public function addToArrayTeacher(&$obj)

[kebbelj]

Interesting-I thought I was passing a reference and not copying a value in PHP 5. Anyway, I tried adding & in both places you suggested and got this message ...

Warning: Call-time pass-by-reference has been deprecated; If you would like to pass it by reference, modify the declaration of runtime function name. If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file in C:\Program Files\wamp\www\db\classes\DB_Administrator.class.php(298) : eval()'d code on line 1

NEW QUESTION PIGGYBACKING ON MY ORIGINAL QUESTION

As long as I'm on the topic of referencing this object inside an array, let me add a related question.

ArrayTeacher is populated by an instance of Teacher named $instanceOfTeacher. If I declared $ArrayTeacher as static, i.e.,

private [SIZE="2"]static [/SIZE]$ArrayTeacher = array();

it would become a property of the class Teacher. This would mean I would use self::addToArrayTeacher($someTeacher) to add it to the array and Teacher::get_ArrayTeacher(12)->get_nameLast() to reference the 12th teacher in the array?

[Weedpacket]

Just a couple of notes:
1) PHP 5 has an "instanceof" operator, which is generally preferable to using is_a().
2) If eval is the answer, then the question is probably wrong 🙂. For example

$class='Teacher';
$teacher = new $class();

is a legitimate way of creating a new Teacher.

What does get_ArrayTeacher() look like?

[kebbelj]

	public function get_ArrayTeacher ( $n )
	{
		return $this->ArrayTeacher[$n];
	}

[kebbelj]

I use eval really heavily in my DB_Adminstrator factory method, which selects information from a MySql table and then contructs an object from each record. Since the factory is meant to be a generic object builder, the class name using it is one of the parameters--$className--sent to factory. factory collects the appropriate database info and builds $fieldstring, the list of property values for the object.

eval gets the job done ANlets me view the constructor by uncommenting the echo statement. (Maybeit doesn't get the job done, however, which is why this thread began. Maybe eval is the problem.)

$evalStatement = $objName." = new ".$className."(".$fieldString.");";
# echo "<br />".$evalStatement;
eval( $evalStatement );

Would this "eval-free" version work as well as the above?

$objName = "Teacher_".$i; // $i being the loop index variable
$objName = new $className($fieldString);

If it does, why would it be superior? (Quicker? etc.)

Thanks.

[Weedpacket]

public function get_ArrayTeacher ( $n )
	{
		return $this->ArrayTeacher[$n];
	}

Well, that certainly return an object if that's what the array contains at that index (and PHP5 has an ArrayAccess interface which, if a class implements it, allows instances to be treated like an array).

public function get_ArrayTeacher ( $n )
	{
die (gettype($this->ArrayTeacher[$n]));
		return $this->ArrayTeacher[$n];
	}

Maybe eval is the problem.

Maybe, since most languages get by fine without it 🙂. It's very easy to get confused about what is code and what is just a string. If you really want to be able to write supergeneric code that generates concrete code, it may be better to separate the two roles; have supergeneric code that writes class files that then get included into the application itself (it's not like they're going to be changing with every script invocation, right?) But I honestly do think that having eval() as a fundamental mechanism for implementing the system architecture is an error.

$objName = "Teacher_".$i; // $i being the loop index variable
$objName = new $className($fieldString);

That would set $objName to a string "Teacher_17" and then set $objName to an instance of whatever $className is.
Have you considered
$objects[$i] = new $className($fieldString);? Of course, $fieldString wouldn't be a string any more, but the actual list of arguments.

[kebbelj]

I normally recognize and follow good advice when I see it, so I ...

1. Replaced

if (is_a($obj, 'Teacher) )

with

if ($obj instanceof $Teacher)

2. Purged my factory method inside DB_Administrator of eval statements. Unfortunately, this command no longer works ...

$objName = new $className($fieldString);

$fieldString is built inside a loop that concatenates a series of field values with

[INDENT]'fieldValue1', 'fieldValue2', 'fieldValue3', 'fieldValue4',[/INDENT]

After the loop ends, I parse off that final comma.

Even though $fieldString echoes as a series of arguments, the constructor sees this series as a single argument and reports it's not getting an argument for 2, 3, 4, etc.

I could solve this problem by modifying the constructor to take the one argument, parse it with the explode function, then feed the Class properties with the array elements from explode. This feels icky because forever afterwards I have to worry about the order of my properties to make sure they're aligning with the right array element. Any future tweaks to the list of arguments and I have a train wreck.

Is there any way to get $fieldString to be seen as a series of values by the constructor instead of one value?