simple question

dmcglone

How do I read this line:

$this->template_dir = TEMPLATE_DIR;

I'm most interested in "$this->"

I don't know how to interpret it. At first glance I thought it was an array, so I looked up arrays in the php manual, but I noticed that an array is in the form such as $alphabet => array("a", "b", "c"........) Which I can clearly read this line as saying "the letters a, b, c,d ........ are all inside the variable $alphabet, but anyway enough rambling, I for some reason thought the line above was also interpreted the same way.

I don't think so....LOL

could anyone shed some light on this for me?

Blessings,

brash

its used in Object-Oriented PHP, and basically it is used to reference the current object. 🙂

halojoy

$this->variable
is used within classes

In the following are 2 class variables: $name and $weight
And has 1 method the function eat()

To refer to such class variables is $this->name used.
In example $units comes from outside of class
and so uses not prefix $this->

<?php

class Bear {

public $name;
public $weight;

public function eat($units) {
    echo $this->name." is eating ".$units." units of food... ";
    $this->weight += $units;
}
}

?>

brash

sorta like in this example of a very simple wrapper method:

public function getNumRow(){
return mysql_num_rows($this->query);
}

all the $this-> is going is saying that query is the current object being referenced.

dmcglone

halojoy;10941666 wrote:
$this->variable
is used within classes

In the following are 2 class variables: $name and $weight
And has 1 method the function eat()

To refer to such class variables is $this->name used.
In example $units comes from outside of class
and so uses not prefix $this->
<?php

class Bear {

public $name;
public $weight;

public function eat($units) {
    echo $this->name." is eating ".$units." units of food... ";
    $this->weight += $units;
}
}

?> 

Thanks Halojoy, in my attempt to understand this furthur, here's what I did:
<?php

class Bear {

public $name;
public $weight;

public function eat($units) {
    echo $this->name." is eating ".$units." units of food... ";
    $this->weight += $units;
}

}

$bear = new Bear();
$bear->eat($units);
?>

I get:
is eating units of food...

I didn't do that correct did I? $name, $weight and $units are missing. I do know they weren't actually defined, so they aren't actually going to display, But then again, I could be wrong.

Blessings,

Ashley_Sheridan

All the variables except $units were defined, but were left with null values.

You can give bear values when you create the object with the __constructor function. Inside the class, create a function like this:

function __constructor($name='Bob', $weight=100)
{
    $this->name = $name;
    $this->weight = $weight;
}

This way, when you create a new Bear() object, it's given a default name and weight, but you can pass new values to it when you create a new Bear object by doing something like this:

$bear = new Bear('Yogi',200);

Hope this helps you!

halojoy

You forgot set some value for $units

Try the class with this

$bear = new Bear();

$bear->name = "BigBrother";

$much = 50;
$bear->eat($much);
echo 'BEAR now weighs ' . $bear->weight . '<br>'; //should give 50

$bear->eat(20);
echo 'BEAR now weighs ' . $bear->weight . '<br>'; //should give 70

Here is a link if you want to study classes in PHP
http://www.phpfreaks.com/tutorial/oo-php-part-1-oop-in-full-effect
🙂

Ashley_Sheridan

I didn't forget to set a value for it, as I figured that dmcglone had struck onto this particular point judging from his last post.

dmcglone

Ashley Sheridan;10941676 wrote:
All the variables except $units were defined, but were left with null values.

You can give bear values when you create the object with the __constructor function. Inside the class, create a function like this:
function __constructor($name='Bob', $weight=100)
{
    $this->name = $name;
    $this->weight = $weight;
}
This way, when you create a new Bear() object, it's given a default name and weight, but you can pass new values to it when you create a new Bear object by doing something like this:
$bear = new Bear('Yogi',200);
Hope this helps you!

It absolutely did. Now I see how to assign the variables values in your example using the constructor.

dmcglone

halojoy;10941677 wrote:
You forgot set some value for $units

Try the class with this
$bear = new Bear();

$bear->name = "BigBrother";

$much = 50;
$bear->eat($much);
echo 'BEAR now weighs ' . $bear->weight . '<br>'; //should give 50

$bear->eat(20);
echo 'BEAR now weighs ' . $bear->weight . '<br>'; //should give 70
Here is a link if you want to study classes in PHP
http://www.phpfreaks.com/tutorial/oo-php-part-1-oop-in-full-effect
🙂

I completely understand now except for one little detail <ducking> How did $much = 50 turn into $bear->weight in the sentence? I see that you defined $much with a value of 50, but boy I have no clue how 50 got into weight.

dmcglone

Ashley Sheridan;10941679 wrote:
I didn't forget to set a value for it, as I figured that dmcglone had struck onto this particular point judging from his last post.

LOL His post was pointing out to me what I forgot. 🙂

dmcglone

Whats your thoughts on this? Any pointers you can give me?

<?php

//This is my exercise to attempt using Classes to try to better understand how classes
//work and also how the keyword "$this" works, so I'm going to build a farm.
//this farm will have 3 characteristics location, size in acres and volume of dairy it produces
//It could eventually be the parent class of things that it contains, such as animals  and the
//various crops it grows. or maybe just the various dairy products it produces.
// But as the production of the dairy or animals increases, so does the size of the farm.

class Farm {
	public $location;
	public $size;
	public $volume;

public function produce($dairy){
$this->size += $dairy;
$this->volume += $dairy;
}
}

$farm = new Farm();
$farm->location = "Columbus, Ohio";
$farm->size = 10; //size of farm in acres
$farm->volume = "1900"; //the volume of dairy products the farm produces a day



$farm->produce($increase);
echo 'The farm is in ' .$farm->location . '<br>'; //I'm expecting columbus, ohio
echo 'today it has grown to ' .$farm->size . ' acres <br>'; //I'm expecting 10
echo 'and produces ' .$farm->volume . ' lbs of dairy products a day. <br><br><br>'; //I'm expecting 1900

$farm->produce(1000);
echo 'Yesterday the farm increased its output volume to '.$farm->volume. ' Dairy products a day <br>'; //I'm expecting 2900
echo 'So the Farmer expanded his land to ' .$farm->size. ' acres to accommodate the growth rate' //I'm expecting 1010

//I see a problem here. It doesn't make sense to expand the farm size by adding the size of the farm to the increased value.
//So to understand this more in depth, I need to figure out how that could be re-written so the size of the farm does not
//necessarily have to be an addition of the increase in produce.

//Would this require another function or could it simply just be a matter of changing operators or creating operands
//to calculate a set growth rate of land based on the volume? Which is basically what is happening now, BUT 1000 acres
//for just 1000 extra pounds of food seems too extreme. By the time the farmer produced enough pounds of food to
//supply plenty of products, his land would probably spread around the world. Now thats a monopoly! LOL


?>

Ashley_Sheridan

Well, you've used an undefined variable $increase. While this will work as a zero value in this specific example, it will throw up a warning.

dmcglone

Ashley Sheridan;10941714 wrote:
Well, you've used an undefined variable $increase. While this will work as a zero value in this specific example, it will throw up a warning.

Hmmm. I didn't get a warning. It did worked, but the increase was by 1000.

dmcglone

dmcglone;10941715 wrote:
Hmmm. I didn't get a warning. It did worked, but the increase was by 1000.

I got it now. I see what you were explaining. I changed the code to this:

class Farm {
	public $location;
	public $size;
	public $volume;
	public $increase;

public function produce($dairy){
$this->size += $dairy;
$this->volume += $dairy;
$this->increase += $dairy;
}
}

$farm = new Farm();
$farm->location = "Columbus, Ohio";
$farm->size = 10; //size of farm in acres
$farm->volume = "1900"; //the volume of dairy products the farm produces a day
$farm->increase = 1;


$farm->produce($increase);
echo 'The farm is in ' .$farm->location . '<br>'; //I'm expecting columbus, ohio
echo 'today it has grown to ' .$farm->size . ' acres <br>'; //I'm expecting 10
echo 'and produces ' .$farm->volume . ' lbs of dairy products a day. <br><br><br>'; //I'm expecting 1900

$farm->produce(1000);
echo 'Yesterday the farm increased its output volume to '.$farm->volume. ' Dairy products a day <br>'; //I'm expecting 2900
echo 'So the Farmer expanded his land to ' .$farm->increase. ' acres to accommodate the growth rate' //I'm expecting 1010

Now I see how I could control the increase.

Would this be the correct solution?

Ashley_Sheridan

It does give a warning, in line 29 (where you have

$farm->produce($increase);

)

Also, The increase by 1000 is only where you call the method explicitly with the value 1000.

dmcglone

dmcglone;10941720 wrote:

I got it now. I see what you were explaining. I changed the code to this:

class Farm {
	public $location;
	public $size;
	public $volume;
	public $increase;

public function produce($dairy){
$this->size += $dairy;
$this->volume += $dairy;
$this->increase += $dairy;
}
}

$farm = new Farm();
$farm->location = "Columbus, Ohio";
$farm->size = 10; //size of farm in acres
$farm->volume = "1900"; //the volume of dairy products the farm produces a day
$farm->increase = 1;


$farm->produce($increase);
echo 'The farm is in ' .$farm->location . '<br>'; //I'm expecting columbus, ohio
echo 'today it has grown to ' .$farm->size . ' acres <br>'; //I'm expecting 10
echo 'and produces ' .$farm->volume . ' lbs of dairy products a day. <br><br><br>'; //I'm expecting 1900

$farm->produce(1000);
echo 'Yesterday the farm increased its output volume to '.$farm->volume. ' Dairy products a day <br>'; //I'm expecting 2900
echo 'So the Farmer expanded his land to ' .$farm->increase. ' acres to accommodate the growth rate' //I'm expecting 1010

Now I see how I could control the increase.

Would this be the correct solution?

Ok I spoke a little too soon.