PHP - Ds Sequence::pop() Function

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The PHPDs\Sequence::pop()function removes the last value in a sequence and returns the previously removed value as a result.

If the current sequence is empty ([]), this function will throw an "UnderflowException". If you try to print the sequence, the last element will be removed from it.

Syntax

Following is the syntax of the PHP Ds\Sequence::pop() function −

abstract public Ds\Sequence::pop(): mixed

Parameters

This function does not accept any parameter.

Return value

This function returns the last removed value.

Example 1

The following is the basic example of the PHP Ds\Sequence::pop() function −

<?php 
   $seq = new \Ds\Vector( [1, 2, 3, 4, 5] );
   echo "The sequence elements are: \n";
   print_r($seq);
   echo "The last removed element: ";
   #using pop() function
   print_r($seq->pop());
?>

Output

The above program produces the following output −

The sequence elements are:
Ds\Vector Object
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
)
The last removed element: 5

Example 2

Pop all the elements one by one using the pop() function within the for-loop.

Following is another example of the PHPDs\Sequence::pop()function. We use this function to remove elements from the last of this sequence (['a', 'e', 'i', 'o', 'u']) −

<?php 
   $seq =  new \Ds\Vector(['a', 'e', 'i', 'o', 'u']);
   echo "The sequence elements are: \n";
   print_r($seq);
   echo "The removed elements are: \n";
   for($i = 0; $i < 5; $i++){ 
      print_r($seq->pop()."\n");
   }
   echo "The sequence after pop each elements: \n";
   print_r($seq);
?>

Output

After executing the above program, the following output will be displayed −

The sequence elements are:
Ds\Vector Object
(
    [0] => a
    [1] => e
    [2] => i
    [3] => o
    [4] => u
)
The removed elements are:
u
o
i
e
a
The sequence after pop each elements:
Ds\Vector Object
(
)

Example 3

If the current sequence is empty ([]), the pop() function will throw an "UnderflowException" −

<?php 
   $seq =  new \Ds\Vector([]);
   echo "The sequence elements are: \n";
   print_r($seq);
   echo "The removed element is: ";
   print_r($seq->pop());
   echo "\nThe sequence after pop last element: \n";
   print_r($seq);
?>

Output

Once the above program is executed, it throws the following exception −

The sequence elements are:
Ds\Vector Object
(
)
The removed element is: PHP Fatal error:  Uncaught UnderflowException: 
Unexpected empty state in C:\Apache24\htdocs\index.php:6
Stack trace:
#0 C:\Apache24\htdocs\index.php(6): Ds\Vector->pop()
#1 {main}
  thrown in C:\Apache24\htdocs\index.php on line 6