6

What is the difference between assigning property values using a constructor and direct property assignment within the class declaration? In other words, what is the difference between the following two pieces of code making default values for the new object?

Code with direct assignment:

<?php
 class A {
   public $name="aName";
   public $weight = 80;
   public $age = 25;
   public $units = 0.02 ;
 }
?>

Code with constructor:

<?php
 class A {
   public $name;
   public $weight;
   public $age;
   public $units;
   public function __construct() {
       $this->name = "aName";
       $this->weight = 80;
       $this->age = 25;
       $this->units= 0.02 ;
   }
 }
?>

You may answer that i can't change the hard coded properties, but i could in the following code( In Local Sever ):

<?php
  class A{
     public $name="aName";
     public $weight = 80;
     public $age = 25;
     public $units = 0.02 ;
  }
 class B extends A{
    public function A_eat(){
       echo $this->name.' '."is".' '.$this->age.' '."years old<br>";
       echo $this->name.' '."is eating".' '.$this->units.' '."units of food<br>";
       $this->weight +=$this->units;
       echo $this->name.' '."weighs".' '.$this->weight."kg";
     }
   }
  $b = new B();
  echo "<p>If no changes to the object's Properties it inherits the main class's</p>";
  $b->A_eat();
  echo '<br><br>';
  echo "<p>If changes made to the object's Properties it uses it's new properties</p>";
  $b->name ="bName";
  $b->weight = 90;
  $b->units = 0.05;
  $b->A_eat();
?>
Mohamed Omar
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  • What is your issue here? For one your constructing method is incorrect anyway, you're missing your bracket braces for deceleration and why would you public something if you're using a method to access it in a setter/getter? – Jaquarh Dec 03 '16 at 06:12
  • Your examples are filled with syntax-errors (`$weight->` for one). That being said, you can't dynamically set values without a constructor. – Qirel Dec 03 '16 at 06:14
  • it was my mistake , i have added the brackets. but my question is why to use constructor will i can give the property a default value in declaration?..please forget about the syntax. – Mohamed Omar Dec 03 '16 at 06:16
  • A constructor method is what **returns** the instanced object. A lot like a configuration method, ie: if you want to load things from the database the same way every time, you'd write it in your `construct()` method.. – Jaquarh Dec 03 '16 at 06:19
  • @MohamedOmar, your question was clear enough without the messy code at the end of the post. – Ruslan Osmanov Dec 03 '16 at 06:32
  • @RuslanOsmanov Sorry! but you know beginners always go through messy stuff – Mohamed Omar Dec 03 '16 at 06:56

6 Answers6

7

When a property declaration contains initialization, the initialization is evaluated at compile time, i.e. in the step when the PHP source is compiled into PHP opcodes.

The code within constructor is evaluated at run time, i.e. at the time when one creates an object with new operator.

There is practically no difference, if you don't use opcode caching (OPcache, APC, and similar extensions). However, if the opcodes are cached, the performance will be better with the compile-time initialization, obviously.

Ruslan Osmanov
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0

Nothing really however,...

in the construct() you could pass in optional variables... for instance..

public function __construct($name = 'aName', $weight = 80, $age = 25, $units = 0.02) {
   $this->name = $name;
   $this->weight = $weight;
   $this->age = $age;
   $this->units = $units;
}

In the first example you posted, you are defining HARD values to your properties, where as in the 2nd one, the construct will let you "build" those...

Take the first example:

$x = new Class(); 
// You can't change it, those properties are what you coded in...

Now look at my example...

$x = new Class('My New Name', 120, 30, 0.10);
// Now $name = 'My New Name' etc...

The construct lets you build the object on initialization rather than hard coding the default values like you had...

You could use the default values and create setters, but I like the __construct()

Roman Lopez
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0

There's nothing major difference between both of these.

Both the approaches are fine, and it basically depends upon your use cases.

According to the first approach you are unable to assign values to class members while creating the Class's object whereas in the 2nd approach you have that power, Let me demonstrate this:

class A
{
    protected $name = 'John';
    protected $age = 20;
}

$obj = new A();
/* Here you get an object with 
** $obj->name = 'John'
** $obj->age = 20;
*/

Whereas in approach 2nd you have the power of defining the variables on the go(while defining its Object). Everytime you create an object for Class B you can have different object everytime based on your passed arguments to the class constructor:

class B
{
    protected $name;
    protected $age;

    public function __construct($name = 'John', $age = 20)
    {
        $this->name = $name;
        $this->age = $age;
    }
}

$obj = new B("John Doe", 40);
/* Here you get an object with 
** $obj->name = 'John Doe'
** $obj->age = 40;
*/

$obj = new B("John Doe");
/* Here you get an object with 
** $obj->name = 'John Doe'
** $obj->age = 20;
*/

Classes which have a constructor method call this method on each newly-created object, so it is suitable for any initialization that the object may need before it is used

Hope this helps!

Saumya Rastogi
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0

Because the constructor can receive parameters to have the object start with values other than some default values. Without a constructor with parameters, you would have to create a default object, then modify it's fields.

Also note there's always a constructor; it's just a question of whether or not you've created one yourself, or a default one is created for you that doesn't require any arguments.

Carcigenicate
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0

A constructor in this case simply puts an object into an active state, allocating proper memory.

One may create a Person object with just a name provided as argument, but another constructor may be needed when both a name and age are given as arguments.

In PHP you are limited to 1 unfortunatly, _contruct

You can have multiple constructors built however in a work around way shown here.

Community
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NSTuttle
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0

What is the difference between a construct method and object properties and when should I use them?

First and foremost, construct() returns an instance of the class you're using, hence why if you ever try return something different inside this method:

public function __construct() { return 'hello, world!'; }

It will not actually work. You're probably asking what this means and why its so important to the question. Well, there are more than just two ways to access data in a property, there are things we call getters and setters.

private $_name;
public function setName($name) { $this->_name = $name; return $this; }
public function getName() { return $this->_name; }

In your use-case, I assume that your data is not constant, it isn't always going to be an age of 25 so you could use multiple ways to approach this. If the data comes from a database, a constructor method would be useful to load the configuration like so:

public $name;
public function __construct($id) { 
    $user = SomeDriver::GetInstance()->on('Users', '*')->where('user_id = ?', [$id]);
    $this->name = $user['username'];
}

Which you can then just access through the instance like $obj->name. However, if you're just setting data through input, you could just use setter/getter or access the properties directly outside the scope;

class User {
    public $name = 'Frank';
    public function setName($name) { $this->name = $name; return $this; }
    public function getName() { return $this->name; }
}

$u = new User;
echo $u->name;
$u->name = 'John';

// or change the property to private and:

$u = new User;
echo $u->getName();
$u->setName('John');
Jaquarh
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