PHP Ds\Queue peek() Function

The Ds\Queue::peek() Function in PHP is used to get the value present at the front of a Queue. This function simply returns the element present at the front of a Queue instance without actually removing it.

Syntax:

mixed public Ds\Queue::peek ( void )

Parameters: This function does not accepts any parameters.

Return Value: This function returns the value present at the front of this Queue. The return type of the function is mixed and depends on the type of value stored in the Queue.

Exception: This function throws an UnderflowException if the Queue is empty.

Below programs illustrate the Ds\Queue::peek() Function in PHP

Program 1:

<?php

// Declare new Queue
$q = new \Ds\Queue();

// Add elements to the Queue
$q->push("One");
$q->push("Two");
$q->push("Three");

echo "Queue is: \n";
print_r($q);

// Get element at the front
echo "\nElement at front is: ";
print_r($q->peek());

?>

Output:

Queue is: 
Ds\Queue Object
(
    [0] => One
    [1] => Two
    [2] => Three
)

Element at front is: One

Program 2:

<?php

// Declare new Queue
$q = new \Ds\Queue ();

echo "Queue is: \n";
print_r($q);

// Get element at the front
echo "\nElement at front is: ";
print_r($q->peek());

?>

Output:

PHP Fatal error:  Uncaught UnderflowException

Reference: http://php.net/manual/en/ds-priorityqueue.peek.php