Destructor method in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a destructor method in a PHP class.

PHP

<?php
class Sample {
    public function [1]() {
        echo "Destructor called";
    }
}
?>

Drag options to blanks, or click blank then click option'

Adelete

B__construct

C__destruct

Ddestruct

Attempts:

3 left

💡 Hint

Common Mistakes

Using __construct instead of __destruct

Omitting the double underscores

Naming the method destruct without underscores

The destructor method in PHP is named __destruct. It is called when an object is destroyed.

2fill in blank

medium

Complete the code to call the destructor automatically when the object is destroyed.

PHP

<?php
class Logger {
    public function __destruct() {
        echo "Closing log file.";
    }
}
$log = new Logger();
[1];

Drag options to blanks, or click blank then click option'

Aunset($log)

Bdelete $log

Cdestroy($log)

Dremove($log)

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete which is not a PHP keyword

Using destroy or remove which do not exist in PHP

Using unset($log) destroys the object and triggers the destructor.

3fill in blank

hard

Fix the error in the destructor method name to ensure it is called properly.

PHP

<?php
class FileHandler {
    public function [1]() {
        echo "File closed.";
    }
}
?>

Drag options to blanks, or click blank then click option'

Adestruct

B__destruct

C__destructor

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using __destructor instead of __destruct

Omitting underscores

Using unrelated names like delete

The correct destructor method name is __destruct. Other names will not be called automatically.

4fill in blank

hard

Fill both blanks to create a class with a destructor that outputs a message when the object is destroyed.

PHP

<?php
class UserSession {
    public function [1]() {
        echo "Session ended.";
    }
}
$session = new UserSession();
[2]($session);

Drag options to blanks, or click blank then click option'

A__destruct

Bunset

Cdelete

D__construct

Attempts:

3 left

💡 Hint

Common Mistakes

Using __construct instead of __destruct

Using delete which is not a PHP function

The destructor method is __destruct. Calling unset($session) destroys the object and triggers the destructor.

5fill in blank

hard

Fill all three blanks to define a class with a destructor that frees a resource and outputs a message when the object is destroyed.

PHP

<?php
class DatabaseConnection {
    private $conn;
    public function __construct() {
        $this->conn = "Connected";
    }
    public function [1]() {
        $this->conn = null;
        echo [2];
    }
}
$db = new DatabaseConnection();
[3]($db);

Drag options to blanks, or click blank then click option'

A__destruct

Bunset

C"Connection closed."

D__construct

Attempts:

3 left

💡 Hint

Common Mistakes

Using __construct instead of __destruct

Not using quotes around the message

Using delete instead of unset

The destructor method is __destruct. It frees the connection and prints the message. Using unset($db) destroys the object and calls the destructor.

Practice

1. What is the purpose of the __destruct method in a PHP class?

easy

A. To clean up resources when an object is destroyed

B. To initialize object properties when created

C. To define a class constant

D. To handle user input validation

Solution

1. Step 1: Understand the role of __destruct

   The __destruct method is called automatically when an object is destroyed or goes out of scope.

2. Step 2: Identify its purpose

   It is used to clean up resources like closing files or database connections safely.

3. Final Answer:

   To clean up resources when an object is destroyed -> Option A

4. Quick Check:

   Destructor method = cleanup on object destruction [OK]

Hint: Destructor cleans up when object is removed from memory [OK]

Common Mistakes:

• Confusing __destruct with __construct
• Thinking it initializes objects
• Using it to handle input validation

2. Which of the following is the correct syntax to declare a destructor method in PHP?

easy

A. function __destruct() {}

B. function destruct() {}

C. function _destruct() {}

D. function __destroy() {}

Solution

1. Step 1: Recall PHP destructor naming

   PHP destructor methods must be named exactly __destruct with two underscores.

2. Step 2: Check syntax correctness

   The correct syntax is function __destruct() {}. Other options have incorrect names.

3. Final Answer:

   function __destruct() {} -> Option A

4. Quick Check:

   Destructor syntax = __destruct() [OK]

Hint: Destructor always starts with double underscores __destruct [OK]

Common Mistakes:

• Using single underscore or wrong method name
• Omitting parentheses in method declaration
• Confusing with __construct method

3. What will be the output of the following PHP code?

class Test {
  function __construct() {
    echo "Constructed\n";
  }
  function __destruct() {
    echo "Destructed\n";
  }
}
$obj = new Test();
echo "Hello\n";
unset($obj);

medium

A. Constructed\nDestructed\nHello\n

B. Hello\nConstructed\nDestructed\n

C. Destructed\nConstructed\nHello\n

D. Constructed\nHello\nDestructed\n

Solution

1. Step 1: Trace object creation and constructor call

   When $obj = new Test(); runs, __construct() prints "Constructed\n".

2. Step 2: Print "Hello" and then unset object

   Next, "Hello\n" is printed. Then unset($obj); destroys the object, triggering __destruct() which prints "Destructed\n".

3. Final Answer:

   Constructed\nHello\nDestructed\n -> Option D

4. Quick Check:

   Constructor then echo then destructor [OK]

Hint: Destructor runs when object is unset or script ends [OK]

Common Mistakes:

• Assuming destructor runs before echo
• Confusing order of constructor and destructor
• Missing that unset triggers destructor immediately

4. Identify the error in this PHP class related to the destructor method:

class Sample {
  function __destruct {
    echo "Cleaning up";
  }
}

medium

A. Destructor must be static

B. Destructor name should be __destroy

C. Missing parentheses in destructor declaration

D. Destructor cannot echo text

Solution

1. Step 1: Check destructor method syntax

   The destructor method must include parentheses even if it has no parameters: function __destruct() {}.

2. Step 2: Identify the missing parentheses error

   The code misses parentheses after __destruct, causing a syntax error.

3. Final Answer:

   Missing parentheses in destructor declaration -> Option C

4. Quick Check:

   Destructor needs () after name [OK]

Hint: Always add () after __destruct method name [OK]

Common Mistakes:

• Omitting parentheses in method declaration
• Using wrong destructor name
• Thinking destructor must be static

5. You want to ensure a file is always closed when your PHP object is destroyed. Which code snippet correctly uses a destructor to do this?

class FileHandler {
  private $file;
  function __construct($filename) {
    $this->file = fopen($filename, 'w');
  }
  // What goes here?
}

hard

A. function __destruct() {
open($this->file);
}

B. function __destruct() {
fclose($this->file);
}

C. function __destruct() {
fclose($filename);
}

D. function __destruct() {
$this->file = null;
}

Solution

1. Step 1: Understand resource cleanup in destructor

   The destructor should close the file resource held in $this->file using fclose().

2. Step 2: Check each option for correctness

   function __destruct() { fclose($this->file); } correctly calls fclose($this->file);. function __destruct() { open($this->file); } tries to open instead of close. function __destruct() { fclose($filename); } uses undefined $filename. function __destruct() { $this->file = null; } just sets property to null without closing.

3. Final Answer:

   function __destruct() { fclose($this->file); } -> Option B

4. Quick Check:

   Destructor closes file resource properly [OK]

Hint: Destructor should close resources like files with fclose() [OK]

Common Mistakes:

• Calling wrong function like open() instead of fclose()
• Using undefined variables inside destructor
• Not actually closing the resource, just nullifying