Is it just me?

JakesSA

Why do these to samples of code that I have written spit out to dirrerent answers, one is object, other is procedural:

/*----------------------------------------------------------------
this prints out  the a integer of 2 as expect, becuase
I have not referenced the the value to the variable.
-------------------------------------------------------------------*/

function doubleValue($var)
      {
	  $var = $var * 2;
	  }
 $variable = 2;
 doubleValue($variable);
 echo $variable; 

//*****************************************


/*----------------------------------------------------------------
but if you take a look at this class you can see how I have called
it..... it prints a integer of 4, without any reference to the value 
-------------------------------------------------------------------*/
 class myClass
   {
	 function setValue($value)
	 {
	 $this->value = $value * 2;
	 }
	 function getValue()
	 {
	 echo $this->value;
	 }
  }	 	 
 $obj = new myClass();
 $attrib = 2;
 $obj->setValue($attrib); 
 $obj->getValue();

can someone please explain to me where I am going wrong with
the code above

Thanks

😉

laserlight

err, your class doesnt have the member variable '$value'

your function doesnt return a value either

perhaps you should use:


function doubleValue($var)
      {
      $var = $var * 2;
      }
 $variable = 2;
 doubleValue(&$variable);
 echo $variable; 

//*****************************************


 class myClass
   {
     var $value;
     function setValue($value)
     {
     $this->value = $value * 2;
     }
     function getValue()
     {
     echo $this->value;
     }
  }          

 $obj = new myClass();
 $attrib = 2;
 $obj->setValue($attrib); 
 $obj->getValue();

JakesSA

err...if you read the question properly, you can see that I have mention

/----------------------------------------------------------------
this prints out the a integer of 2 as expect, becuase
I have not referenced the the value to the variable.
-------------------------------------------------------------------/

Why is the class spitting out the value of 4?

JakesSA

err...if you read the question properly, you will see that I have mention it.

/----------------------------------------------------------------
this prints out the a integer of 2 as expect, becuase
I have not referenced the the value to the variable.
-------------------------------------------------------------------/

My question is why is the class assigning the value from attrib to value without reference....surely the value should be lost.

Were is the mistake

laserlight

well, my explanation would be that the interpreter initialized a member variable $value when it was assigned to in setValue()

sorry though, your example didnt follow code that I would normally expect so I assumed you had typos.

JakesSA

but surely the value of $attrib would be lost in the class because it has not been referenced to $value. It should have been passed and then lost like the procedural code
:eek:

laserlight

um, $attrib is passed by value to the setValue member function which assigns that value to the local variable $value which is then assigned, with an arithmetic operation, to the apparently non-existent member variable $value.

My conclusion therefore is that the non-existent member variable $value is initialized and then available to the whole object since it is, after all, a member variable.

EDIT:
whoops, "whole object", not "whole class"

TruckStuff

but surely the value of $attrib would be lost in the class because it has not been referenced to $value.

Not neccesarily. If PHP sees that a variable (and apparently member attributes) has not been defined yet, it assume you want to create one and perform the stated operation.

The first example works because the $var and $variable never touch eachother (variable scope). The second works properly because you are referencing the same attribute in the same object, therefore its the same. 🙂

JakesSA

to me it should still not pick it up, say you set the member ($value) to zero, you are passing that variable ($value set to 0) to the method by value -- as this is how variables are passed around, unless otherwise stated with the reference "&" parameter.... not where in the object has that been done.

 class myClass
   {
     var $value = 0; #<-setting the member to zero

 function setValue($value)
 {
 $this->value = $value * 2;
 }
 function getValue()
 {
 echo $this->value;
 }
  }	 	 
 $obj = new myClass();
 $obj->setValue($attrib = 2); 
 $obj->getValue();

when you add reference to it, you get the same answer...which is the answer orginally expected.

laserlight

Um, you're 2nd example is perfectly ok.
What are you talking about passing by reference?
You never did pass by reference.

My argument for it not working was that the member variable $value didnt even exist.
Since it worked, logic implies that it must exist, so it must have been created when assigned, i.e. PHP's "initialize variables being assigned to if they are not assigned" philosophy.
Since this newly initialized variable is a member variable, it is available to all member functions.

say you set the member ($value) to zero, you are passing that variable ($value set to 0) to the method by value

That is initialization. It isnt passing as an argument.
I think you are getting confused between function arguments and the relationship between member functions and member variables in a class.

JakesSA

So did the first, thats my point!!!

How are variables passed in PHP? By value or by reference?

Yes, you got it....by value!!!

I have passed $attrib to $value by value (in the example its 2), and please NOTE: laserlight only initialized the member to use within the method.

....$atrrib should be lost... no connection was made between the two, unless I use the reference operator "&" ....this is clearly shown in the following code:

// answer -> variable = 2,  becuase it was lost function never
// changed the scope

function doubleValue($var)
      {
      $var = $var * 2;
      }
 $variable = 2;
 doubleValue($variable);
 echo $variable; 

// answer -> variable = 4,  because the function changed the 
//scope

function doubleValue(&$var)
      {
      $var = $var * 2;
      }
 $variable = 2;
 doubleValue($variable);
 echo $variable;

Now tell me why this is not happening in the object. Please use some code to explain yourself....

JakesSA

check out Zend Engine 2 Workshop @ Zend...

laserlight

I have passed $attrib to $value by value

yes, didnt I mention that in an earlier post?

Look again at your most recent example.
Is it object oriented? No.

There are no member variables, there are no member functions.
Only functions and local variables, aside from the variables declared as per normal procedual programming.

What is an object?
It is an instance of a class, where a class can be seen as a datatype containing a blueprint for data and methods to deal with the data.
As such, if the member variable is indeed initialized with a member function, it is available to the whole object.
I thought it wasnt unless declared explicitly, but I was wrong since your original example showed otherwise.

Use:

class myClass
   {
     var $value = 0; #<-setting the member to zero

 function setValue($value)
 {
 $value = $value * 2;
 }
 function getValue()
 {
 echo $this->value;
 }
  }          

 $obj = new myClass();
 $obj->setValue($attrib = 2); 
 $obj->getValue();

No more member variable initialized in setValue()
Suddenly, $obj->getValue() outputs 0
I dont even have to test to be certain of that.

laserlight

Perhaps I shall clarify further.

function myfunc($arg1) {
	//$arg1 is a local variable
	$arg1 = $arg1; //duh
}
function getArg() {
	return $arg1;
	//but $arg1 doesnt exist
	//so there may be a notice of an un-initialized variable
	//and this is the same as return NULL
}

class MyClass {
	var $argument;
	function myfunc($arg1) {
		//$arg1 is a local variable
		//$argument is a local variable
		$argument = $arg1;
		//but $this->argument is a member variable
		$this->argument = $arg1;
	}
	function getArg() {
		//there's no argument
		//$this->argument is used just like this:
		return $this->argument;
		/*
		does it mean that it is always the same as return NULL ?
		no, for if $this->myfunc() is used first,
		then the value passed to $this->myfunc() would be returned

	but it wasnt passed by reference!
	but $this->argument is a member variable, hence it is
	available to $this->getArg() as well
	*/
}
}

JakesSA

obie kanobie is calling laserlight ... dont bother. You code doesnt prove the point Im trying to get @.

laserlight

Could you please state your point more clearly then?

I mean, I'm not obliged to prove a point, I've only taken up the responsibility to explain what I think is happening.

If you want to win an argument, go ahead, win it.
I dont lose anything, and I just gain my post count 😃

If you want help with understanding code from a different viewpoint, ask.