How to use constructors in php to initialize instance variables

Question

I know that this is a common question but the questions I've seen (about 10) confused even more than I've been.

My questions are included in the code as comments.

I have a class with three fields

public class Model
{
    public $prop1;
    public $prop2;
    public $prop3;

     public function _construct($params)  // doubt 1: Do I have to pass an array to a constructor, can't I pass the parameters individually
       {
                // doubt 2: How to assign the value to the instance variables
       }
}

$model = new \App\Model($whatToPuthere); //doubt 3: How to provide the constructor parameters

Have you read the PHP documentation about Classes and Objects? Everything you need to know for now is explained there, with examples. — axiac
– axiac, Commented Aug 28, 2017 at 15:19
There's a documentation for everything" If we follow this line of thinking there's no reason to have stackoverflow. If I stop to read the documentation for every problem I face it will take a long long time to complete my tasks. My question is very basic concept that one should have under his belt but in this moment I don't have the time to read the documentation. — Diego Alves
– Diego Alves, Commented Aug 28, 2017 at 15:30
Besides I read the documentation but I got confused by it too. Constructor in PHP is very confusing for me. You should have asked if I read the docs, before the downvote! — Diego Alves
– Diego Alves, Commented Aug 28, 2017 at 15:39

yoeunes · Accepted Answer · 2017-08-28 15:35:17Z

1

the proper way to do it is like :

public class Model
{
    public $prop1;
    public $prop2;
    public $prop3;

     public function __construct($prop1, $prop2, $prop3)  
     {
          $this->prop1 = $prop1; 
          $this->prop2 = $prop2; 
          $this->prop3 = $prop3; 
     }
}

$model = new \App\Model("prop1_value", "prop2_value", "prop3_value");

edited Aug 28, 2017 at 15:35

answered Aug 28, 2017 at 15:13

yoeunes

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7 Comments

Sahil Gulati Over a year ago

Please add explanation too.

Anis Alibegić Over a year ago

Your code is invalid. Your construct method is invalid.

Anis Alibegić Over a year ago

Still not ready to upvote... $this->prop1 = $props1;... are you sure $props1 exists? :)

Anis Alibegić Over a year ago

Look better. You are passing $prop1 but using $props1 while assigning.

yoeunes Over a year ago

@Spectarion you're right sir, i'm really tired i didn't see it, good catches (y)

|

Vilsol · Accepted Answer · 2017-08-28 15:18:28Z

0

You were pretty close, to access the current instance variables, you need to use $this. You also need to use 2 underscores for the construct method. Other than that, treat it as just another function.

class Model {

    public $prop1;
    public $prop2;
    public $prop3;

    public function __construct($prop1, $prop2, $prop3) {
        $this->prop1 = $prop1;
        $this->prop2 = $prop2;
        $this->prop3 = $prop2;
    }

}

$model = new \App\Model("prop1", "prop2", "prop3");

answered Aug 28, 2017 at 15:18

Vilsol

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Comments

Plamen Nikolov · Accepted Answer · 2017-08-28 15:43:00Z

0

It is up to you to decide what is more convenient for your \App\Model class users. Here is an example working with fixed number of properties.

class Model
{
    public $prop1;
    public $prop2;
    public $prop3;

     public function __construct($prop1, $prop2, $prop3)
     {
       $this->prop1 = $prop1;
       $this->prop2 = $prop2;
       $this->prop3 = $prop3; 
     }
}

$model = new \App\Model('Property 1', 'Property 2', 'Property 3');

If you intend to work with dynamic number of properties, you should consider using array as parameters.

class Model
{
    public $prop1;
    public $prop2;
    public $prop3;

     public function __construct(array $properties)
     {
         $this->prop1 = $properties['prop1'];
         $this->prop2 = $properties['prop2'];
         $this->prop3 = $properties['prop3']; 
     }
}

$model = new \App\Model(
   array('prop1' => 'Property 1', 'prop2' => 'Property 2', 'prop3' => 'Property 3')
);

edited Aug 28, 2017 at 15:43

answered Aug 28, 2017 at 15:18

Plamen Nikolov

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1 Comment

B001ᛦ Over a year ago

public classis not valid!

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