Destructor method in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP destructor example?

Consider the following PHP code. What will it output when run?

PHP

<?php
class Test {
    public function __construct() {
        echo "Constructed\n";
    }
    public function __destruct() {
        echo "Destructed\n";
    }
}
$obj = new Test();
echo "End of script\n";
?>

A

Constructed
Destructed
End of script

B

Constructed
End of script
Destructed

C

Destructed
Constructed
End of script

D

End of script
Constructed
Destructed

💡 Hint

Remember that the destructor runs when the object is destroyed, usually at the end of the script.

The constructor runs first, printing "Constructed". Then the script prints "End of script". Finally, when the script ends and the object is destroyed, the destructor prints "Destructed".

❓ Predict Output

intermediate

What happens when an object is unset explicitly?

What will this PHP code output?

PHP

<?php
class Sample {
    public function __destruct() {
        echo "Bye!\n";
    }
}
$obj = new Sample();
unset($obj);
echo "After unset\n";
?>

A

Bye!

B

After unset
Bye!

C

Bye!
After unset

D

After unset

💡 Hint

Think about when the destructor is called if you unset the object manually.

When you unset the object, the destructor runs immediately, printing "Bye!". Then the script prints "After unset".

🔧 Debug

advanced

Why does this destructor not run as expected?

Look at this PHP code. The destructor message is never printed. Why?

PHP

<?php
class Demo {
    public function __destruct() {
        echo "Destroying\n";
    }
}
function create() {
    $obj = new Demo();
}
create();
echo "Done\n";
?>

A The destructor is not called because PHP requires explicit unset to run destructor.

B The destructor is never called because the object is inside a function and goes out of scope silently.

C The destructor is called but output is buffered and not shown.

D The object is destroyed immediately after create() ends, so destructor runs before echo "Done".

💡 Hint

Think about when local variables inside functions are destroyed.

The object $obj is destroyed as soon as the function create() finishes, so the destructor runs before the "Done" message is printed.

📝 Syntax

advanced

Which option shows the correct destructor syntax in PHP?

Choose the correct way to declare a destructor method in a PHP class.

A public function __destruct() {}

B public function destruct() {}

C function __destruct {}

D public function ~destruct() {}

💡 Hint

Destructor method name must be exactly __destruct with parentheses.

In PHP, the destructor method must be named __destruct with parentheses and a function body.

🚀 Application

expert

What is the output when multiple objects with destructors are created and unset?

Consider this PHP code. What will be the exact output?

PHP

<?php
class A {
    public function __destruct() {
        echo "A destroyed\n";
    }
}
class B {
    public function __destruct() {
        echo "B destroyed\n";
    }
}
$a = new A();
$b = new B();
unset($a);
echo "Middle\n";
?>

A

A destroyed
Middle
B destroyed

B

Middle
A destroyed
B destroyed

C

A destroyed
B destroyed
Middle

D

B destroyed
A destroyed
Middle

💡 Hint

Think about when each object is destroyed and when the script ends.

When unset($a) runs, A's destructor prints "A destroyed". Then "Middle" is printed. At script end, B's destructor runs, printing "B destroyed".

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