How to initialize variable in constructor in PHP - php

Question

I am writing this simple code and do not know what the issue with constructor is:
class Animal {
public $_type;
public $_breed;
public function __construct ($t, $b) {
echo "i have initialized<br/>";
$this ->_type = $t;
$this ->_breed = $b;
echo "type is " .$_type. "<br/>";
echo "breed is " .$_breed. "<br/>";
}
public function __destruct () {
echo "i am dying";
}
}
$dog = new Animal("Dog", "Pug");

Answer 1

Why do you have a space after $this? Remove the space.
Also, add $this when calling a variable.
class Animal {
public $_type;
public $_breed;
public function __construct ($t, $b) {
echo "i have initialized<br/>";
$this->_type = $t; // <-- remove space
$this->_breed = $b; // <-- remove space
echo "type is " .$this->_type. "<br/>"; // <-- add $this
echo "breed is " .$this->_breed. "<br/>"; // <-- add $this
}
public function __destruct () {
echo "i am dying";
}
}

Answer 2

You are initializing them fine, but retrieving them wrong...
Since $_type and $_breed are scoped at the object level, you need to tell PHP what scope you're referencing them in.
Therefore, instead of
echo $_breed;
You need
echo $this->_breed;
On a side note, it's very strange practice to prefix variable names with _ these days, even moreso if they are public variables. This will likely confuse other developers working with your code.

Answer 3

Try this (note the echo lines):
class Animal {
public $_type;
public $_breed;
public function __construct ($t, $b) {
echo "i have initialized<br/>";
$this->_type = $t;
$this->_breed = $b;
//You have to use '$this' keyword to access
//class attibutes:
echo "type is " . $this->_type . "<br/>";
echo "breed is " . $this->_breed . "<br/>";
}
public function __destruct () {
echo "i am dying";
}
}

Answer 4

$_type and $_breed is variable of class so you need to use using this keyword
echo "type is " .$this->_type. "<br/>";
echo "breed is " .$this->_breed. "<br/>";

Answer 5

Although this not violate the syntax of the php, I suggest that this two lines
echo "type is " .$dog->_type. "<br/>";
echo "breed is " .$dog->_breed. "<br/>";
must not be put in __construct() instead use this outside the class,
Like this,
class Animal {
public $_type;
public $_breed;
public function __construct ($t, $b) {
$this ->_type = $t;
$this ->_breed = $b;
}
public function __destruct () {
echo "i am dying";
}
}
$dog = new Animal("Dog", "Pug");
echo "i have initialized<br/>";
echo "type is " .$dog->_type. "<br/>";
echo "breed is " .$dog->_breed. "<br/>";

Answer 6

With constructor property promotion in PHP 8, you can now declare and set properties as parameters of the constructor.
See here.
class someClass
{
// Can delete these declarations and put them in the constructor instead //
/*
protected int $id;
protected string $name;
protected int $type;
protected string $frontend_name;
protected int $account_id;
protected someOtherClass $object;
*/
public function __construct(
protected int $id,
protected string $name,
protected int $type,
protected string $frontend_name,
protected int $account_id,
protected someOtherClass $object,) // you can also have a trailing comma now!
{
$this->init();
}
protected function init() {
// do other stuff
}
}