Why do we have default values for class properties?

Question

If we do not pass in arguments in our echo statement, we get an error instead of seeing the default values displayed. So i'm confused. I get why we are declaring the properties, but do not understand why we are giving them default values.

class Product {
    public $name = 'default name';
    public $price = 0;
    public $desc = 'default description';

    function __construct($name, $price, $desc) {
        $this->name = $name;
        $this->price = $price;
        $this->desc = $desc;
    }

    public function getInfo() {
        return "Product Name: ". $this->name;
    }
}

$testObj = new Product("James Brown", 1000, "The most amazing man");

echo $testObj->getInfo();

Answer 1 · 2015-01-05T05:20:28Z

January 5, 2015 5:20am

Depending on your application, there's no need for a default value. I think a potential reason for giving a default value would be to use the default value as part of a conditional check:

<?php
class Example {
    public static $name = "doug";

    function __construct($name=null) {

//Checks value of $name, if it doesn't equal the default value 
//then set the argument passed into Example() as $name

        if ($name != "doug") 
        {

            $this->name = $name;
        }
        else 
        {
            $this->name = self::$name;
        }
   }
    public function get() {
    if (is_null($this->name)) {
    return "No name given";
    }
    return $this->name;
    }
}

$test = new Example("frank");

echo $test->get();
?>

Answer 2 · 2015-01-05T06:06:19Z

January 5, 2015 6:06am

Sometimes it is good to give a default value so that when coding you don't have to explicitly set that default value when creating that object & consequently saving it to the db.. saves you some lines..

Here is an example.. usually on websites they may have a user status (which could be live|banned|need_activation.. and you would set this to last one in this case as newly registered user would need to activate their account by clicking on a link in the email..

Another one would be user type.. again a newly registered user would most likely be a user and not admin or a mod.. so you could set that to default value of user..

In the end you don't have to have a default value (Like mentioned above) if it doesnt make sense for your application.

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carlosjimenez

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Why do we have default values for class properties?

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Adam Young

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