$this

[wolf73]

I am trying to learn OO PHP. I get really confused looking at the code. I don't understand what detremine that we will use $this or not.
Like in the codde below.





if(($check_stage<=$called_stage)&&(!$errors_detected))
{
$this->model[$check_stage]->check_required_fields();

/**
* Check if any errors are loaded into the rf_error_codes array
*/
if(count($this->model[$check_stage]->rf_error_codes))
{
$this->errors = array_merge($this->errors,$this->model[$check_stage]->rf_error_codes);
/**
* Validation errors were detected for this model, we want to send the user to this
* step.
*/
$this->stage = $check_stage;

/**
* Set the errors detected flag, so we won't save the data or increment the stage
* counter. However, we want to continue looping and and building data for each model,
* so that to the user it will appear we're saving their data. When they return to the page
* the fields will be pre-filled with anything they've filled out so far.
*/
$errors_detected = true;
}


why not use $this in first if statment , like below.


if(($this->check_stage<=$called_stage)&&(!$errors_detected))

on what bases they decided not to us $this.


same way what made them decide use
$this->stage = $check_stage; not $stage = $check_stage;

and use
$errors_detected = true; NOT $this->errors_detected = true;

 

[sleipnir214]

Let's use a simple class:

class Fi
{
	var $fy;

	function fo ($fum)
	{
  		$fubar = 3;
		if ($this->fy == $fubar + $fum)
		{
			print "yahoo";
		}
	}
}

The interesting bit is the line:

[tt]if ($this->fy == $fubar + $fum)[/tt]

which compares the class-level variable $fy (defined in the "var $fy" line and referenced as $this->fy) to the sum of the method-level variables $fubar and $fum (defined by explicit assignment or as the input parameter of the method, respectively).

Your script excerpt doesn't specify at what level the variables in question were declared, so I can only guess that in this line:

[tt]if(($check_stage<=$called_stage)&&(!$errors_detected))[/tt]

the comparison is between variables that are defined at the method-level.



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[wolf73]

SO are you saying when a class level variables referenced in a function it should be refernced as $this,
what will happen if in your exapmple if you do it as
($fy == $fubar + $fum)

 

[sleipnir214]

I assume you mean within the conditional in the method:

[tt]if ($fy == $fubar + $fum)[/tt]

so that the class definition would look like:

class Fi
{
    var $fy;

    function fo ($fum)
    {
          $fubar = 3;
        if ($fy == $fubar + $fum)
        {
            print "yahoo";
        }
    }
}

Since [tt]$fy[/tt] inside the method must reference a method-level variable (there's no "$this->") and since that variable does not exist, PHP will throw a Notice about the use of a non-existent variable used in a condition. Something like:

Notice: Undefined variable: fy in /path/to/script/script.php on line <line number>

Script execution will continue, though.



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[wolf73]

Thanks I got it, now following statment is with in a method.
Now they are creating an object


$this->form_field = new FormField();

What will be the reaon for doing it this way why not
$form_field = new FormField();

 

[sleipnir214]

I don't know. Maybe the authors of the code wanted to initialize a class-level variable?


Do you understand the difference in length of existence between class-level variables and method-level variables?

Take the following script:

<?php
class A
{
    var $a;

    function set_function_level_a ($b)
    {
    	$a = $b;
    }
    
    function set_class_level_a ($b)
    {
    	$this->a = $b;
    }
    
    function show_all_a ()
    {
    	print '$a:' . $a;
    	print '<br>';
    	print '$this->a:' . $this->a;
    }
}

$a = new Fi();
$a->set_function_level_a(1);
$a->set_class_level_a(2);

show_all_a();
?>

The output of the script is:

[tt]Notice: Undefined variable: a in /home/sites/test/html/test_bar.php on line 18
$a:
$this->a:2[/tt]

The script generates the Notice in show_all_a() because the variable does not exist. $this->a exists, because class-level variables exist for the length of the existence of the object. $a does not, because method-level variables only exist for the length of the run of their respective methods.

$a exists and is assigned a value in set_function_level_a(), but ceases to exist as soon as the method quits running. When show_all_a() attempts to reference $a, it correctly produces the error because the method-level $a does not exist -- there has been no statement within show_all_a() which would make $a exist.



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[wolf73]

Thanks, Got it, now instead of declaring the variable at the top in the class will that be acceptable (just doing it straight in the method)
<?php
class A
{
function set_function_level_a ($b)
{
$a = $b;
}

function set_class_level_a ($b)
{
$this->a = $b;
}

function show_all_a ()
{
print '$a:' . $a;
print '<br>';
print '$this->a:' . $this->a;
}
}

$a = new Fi();
$a->set_function_level_a(1);
$a->set_class_level_a(2);

show_all_a();
?>

 

[sleipnir214]

It will work, I think. But it's piss-poor programming style. And I have no idea how your idea will work once you add PHP's class variable visibility modifiers (public, private, protected) to the mix.

I strongly recommend that you declare class-level variables at the top of the class definition.




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[wolf73]

i see this code

class YespaydayController extends BasicSiteController
{

protected function process_step1()
{

/**
* Creates a PostedLead object with most fields pre-filled
*/
$this->postedlead = $this->get_posted_lead();


}


}

here get_posted_lead(); is function in the class BasicSiteController, I was wondering why we calling the function like this why not

$this->postedlead = get_posted_lead(); ?

 

[sleipnir214]

Because that's how you call a class method.

If you did:

$this->postedlead = get_posted_lead();

you'd be calling a function that is not a class method.

Run this test script:

<?php
function bar ()
{
	print "function bar\r\n";
}

class foo
{
	function bar ()
	{
		print "method bar\r\n";
	}
	
	function baz()
	{
		print "method baz\r\n";
		
		bar();
		
		$this->bar();
	}
}

$a = new foo();

print '<html><body><pre>';
$a->baz();
print '</pre></body></html>';
?>

It should output:

method baz
function bar
method bar





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[wolf73]

Thanks a lot, I understand now

 

[wolf73]

i have a question about the following .... here in the line last line , are we creating an object from a class PostedLead and passing a variable to the constructor and then returning that object, right?



protected function get_posted_lead()
{
/**
* Set up PostedLead, with data from the current lead
*/

$attributes = Array(
"session_id" => $this->lead->session_id,
"cluster_id" => $this->lead->cluster_id,
"offer_id" => $this->lead->offer_id,
"site_id" => $this->lead->site_id,
"affiliate_id" => $this->lead->affiliate_id,
"sub" => $this->lead->sub,
"sub2" => $this->lead->sub2,
"email" => $this->lead->email,
"phone" => $this->lead->phone
);

return new PostedLead($attributes);
}

 

[sleipnir214]

Probably. I don't know enought about the rest of the code involved to answer more definately.



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