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JasonDavis
JasonDavis

Reputation: 48973

When to use $this->property instead of $property in PHP

Super easy question. Look at the 2 sample class methods.

In the first One I pass in a variable/property call $params I then do $this->params

My question is, is it really needed, I generally do it this way but I have noticed that it will work in the second example with just calling $params without setting $this to it.

So my theory is this... You have to set it like $this->params if you need to access that property in a different method in that class and you can use just $params if you are only using that property in that same method it is in already.

Could somebody shed some light on this and explain if my theory is correct or if I am way off I would like to know the reasoning for this so I will know when do do each method or to do one or the other all the time, thanks you

class TestClass{

    public function TestFunc($params){
       $this->params = $params;

       echo 'testing this something'. $this->params;
    }
}

without defining variables

class TestClass2{

    public function TestFunc2($params){
       echo 'testing this something'. $params;
    }
}

Upvotes: 4

Views: 3931

Answers (5)

Gordon
Gordon

Reputation: 317147

Your own theory

You have to set it like $this->params if you need to access that property in a different method in that class and you can use just $params if you are only using that property in that same method it is in already.

is a good guideline, but it falls somewhat short. Consider

public function applyDiscount($discount)
{
    if ($this->isValidDiscountRangeForProduct($discount)) {
        $this->price -= $this->price * $discount;
    }
}

You would not assign $discount to an object property just because you needed to validate it before applying it to the $this->price (use in other method). A better guideline would be

If the argument is only used to calculate internal state of the object, you don't make it a property.

Also, keep in mind that a method like your

public function TestFunc2($params)
{
   echo 'testing this something' . $params;
}

is likely misplaced on that object because it has no cohesion. You only want methods on your object that operate on the data of this object in some way. Attaching methods that do not operate on the object members is like tucking an ice crusher onto your car:

class Car 
{
    public function crushIce($ice)
    {
        // WTF!?
    }
}

Further resources:

Upvotes: 0

Nonym
Nonym

Reputation: 6299

Use $this when accessing class variables.

When accessing a variable which is actually a parameter in a function, there's no need to utilize the $this keyword.. Actually, to access the function parameter named $params, you should not use the $this keyword...

In your example:

class TestClass{

    public function TestFunc($params){
       $this->params = $params;

       echo 'testing this something'. $this->params;
    }
}

$params from TestFunc($params){ is a parameter/argument of the function TestFunc and so you don't need to use $this. In fact, to access the parameter's value, you must not use $this -- Now when you used $this->params from $this->params = $params = $params;, you are actually setting a value equivalent to that of the parameter $params to a NEW class-level variable named also $params (since you didn't declare it anywhere in your sample code)

[edit] based on comment:

Look at this example:

class TestClass{

    public function TestFunc($params){
       $this->params = $params;
       # ^ you are setting a new class-level variable $params
       # with the value passed to the function TestFunc 
       # also named $params

       echo 'testing this something'. $this->params;
    }

    public function EchoParameterFromFunction_TestFunc() {
        echo "\n\$this->params: " . $this->params . "\n";
        # now you are echo-ing the class-level variable named $params
        # from which its value was taken from the parameter passed
        # to function TestFunc
    }

}

$tc = new TestClass();
$tc->EchoParameterFromFunction_TestFunc(); # error: undefined property TestClass::$params
$tc->TestFunc('TestFuncParam');
$tc->EchoParameterFromFunction_TestFunc(); # should echo: $this->params: TestFuncParam

The error when you called EchoParameterFromFunction_TestFunc without first calling TestFunc is a result of not declaring/setting the class-level variable/property named $params --you set this up inside TestFunc, which means it doesn't get set unless you call TestFunc. To set it right so that anyone can immediately access it is to:

class TestClass{
    # declare (and set if you like)
    public /*or private or protected*/ $params; // = ''; or create a construct...

    public function __construct(){
        # set (and first declare if you like)
        $this->params = 'default value';
    }
...
...
...

[edit : additional]

As @liquorvicar mentioned, which I also totally agree with is that you should always declare all your class-level properties/variables, regardless of whether or not you will use them. Reason being and as an example is that you don't want to access a variable that hasn't been set. See my example above which threw the error undefined property TestClass::$params..

Thanks to @liquorvicar for reminding me..

Upvotes: 9

maček
maček

Reputation: 77796

I hope this will help clear things up:

class Person {

   private $name;
   private $age;

   public function __construct($name, $age){
     // save func params to instance vars
     $this->name = $name;
     $this->age = $age;
   }

   public function say_hello(){ // look, no func params!
     echo "My name is {$this->name} and I am {$this->age} years old!";
   }

   public function celebrate_birthday(){ // no params again
     echo "Party time!";
     $this->age += 1; // update instance var
     $this->drink_beer();  // call instance method
   }

   public function drink_beer(){
     echo "Beer is good!";
   }
}

$p = new Person("Sample", "20");
$p->say_hello();          // My name is Sample and I am 20 years old!
$p->celebrate_birthday(); // Party time! Beer is good!
$p->say_hello();          // My name is Sample and I am 21 years old!

Upvotes: 2

matino
matino

Reputation: 17725

You have already answered your question yourself:

You have to set it like $this->params if you need to access that property in a different method in that class and you can use just $params if you are only using that property in that same method it is in already

Upvotes: 1

Shai Mishali
Shai Mishali

Reputation: 9402

In general you can use specific variable when they're in the context ("scope") of your object.

In OOP programming, $this will almost always be used to access a class variable or other class method.

class MyClass{
     private $myNum;

     public function myFunc(){
          echo 'My number is '.$this->myNum; // Outputting the class variable "myNum"
     }

     public function go($myNumber){
          $this->myNum  = $myNumber; // Will set the class variable "$myNum" to the value of "$myNumbe" - a parameter fo the "go" function.
          $this->myFunc(); // Will call the function "myFunc()" on the current object
     }
}

Shai.

Upvotes: 1

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