help to understand $this in OOP

[azegurb]

I hava script with both $this keyword and without it. Each one does the same thing.
I cant understand what does $this do.
this with $this

class Time {

  var $sTime;

  function GenerateCurrentTime(){
    $this->sTime = gmdate("d-m-Y H:i:s");
    return $this->sTime;
  }

  function ShowFutureDate($iAddDays=0){
    $this->sTime = gmdate("d-m-Y H:i:s", strtotime("+" . $iAddDays . " days"));
    return $this->sTime;
  }
}

and this is without $this version

class Time {

  var $sTime;

  function GenerateCurrentTime(){
    $sTime = gmdate("d-m-Y H:i:s");
    return $sTime;
  }

  function ShowFutureDate($iAddDays=0){
    $sTime = gmdate("d-m-Y H:i:s", strtotime("+" . $iAddDays . " days"));
    return $sTime;
  }
}

Thanks in advance for attention

[dcdruck]

Use $this if you want to update the value of that particular property of the object (if you want to save the value). If you want to use $sTime just in that function to compute a time, return it, and forget about it, then don't use $this.

mypage.php

require('time.class.php'); // replace this with the filename of your class

$mytime = new Time();
echo '<div>Before time: ' . $mytime->sTime . '</div>'; // should be empty or null

$mytime->GenerateCurrentTime();

/* If your function says $this->sTime, the time will show up here. If your function instead uses $sTime (no $this), the time will again be empty or null here. */
echo '<div>After time: ' . $mytime->sTime . '</div>';

[azegurb]

thank you very much. Is it true when we use with this it is not necessary to use return statement?

[dcdruck]

It entirely depends on what your function is doing. For example, if I'm writing a function to set the value for $firstname in an object person, then there's probably no need to return anything. On the other hand, if I were writing a function to retrieve the value of $firstname, then I would absolutely need a return statement. See the following example class Person:

class person
{
  var $firstname;
  var $lastname;

  function __construct()
  {
    $this->firstname = '';
    $this->lastname  = '';
  }

  function setFirstname(firstname)
  {
    // since I'm just setting the value right now and not using it
    // there's no need to return anything.
    $this->firstname = firstname;
  }

  function getFirstname()
  {
    return $this->firstname;
  }
}

[mschroeder]

I agree it entirely depends on what the function is doing. However I disagree with the code example. If you're going to write classes you should be using PHP 5 syntax.

• No reason to have a constructor as the variables default to 'NULL' you could also default them in the class.
• Variables and functions should have scope, public/protected/private etc.
• If you're not going to return anything from your function returning $this will allow you to chain your method calls together. See Below

class person
{
  public $firstname = '';
  public $lastname = '';

  public function setFirstname( $firstname )
  {
    $this->firstname = $firstname;
    return $this;
  }

  public function getFirstname()
  {
    return $this->firstname;
  }
}

By returning $this from functions that don't have a return value, usually setters, you can chain the method calls together.

<?php
$person = new person();
echo $person->setFirstname('John')->getFirstname(); //John
echo $person->setFirstname('John')->setFirstname('Joe')->setFirstname('Bill')->getFirstname(); //Bill

This example is not a very good example of method chaining but take something like the following example:

<?php

class Person
{
  public $firstName;
  public $lastName;
  public $birthday;

  public function setFirstname( $name ){ ... }
  public function setLastname( $name ){ ... }
  public function setBirthday( $bday ){ ... }
}

Each setter function would return $this. By using method chaining we can keep calling methods on the return of each function as each function will always return a reference to itself.

e.g.

<?php
$person = new Person();
$person->setFirstname('John')
       ->setLastname('Doe')
       ->setBirthday('01/01/2011');

There is no benefit to this over just calling $person->method(); in multiple statements, but this is something I see that few people know about.

[azegurb]

i have read from internet that here is not necessary
return like below.

class Time {

  var $sTime;

  function GenerateCurrentTime(){
    $this->sTime = gmdate("d-m-Y H:i:s");
  }

  function ShowFutureDate($iAddDays=0){
    $this->sTime = gmdate("d-m-Y H:i:s", strtotime("+" . $iAddDays . " days"));
  }
}

Is it true. or somebody has written this false
thank you for attention