PHP - Ds\PriorityQueue::allocate() Function

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The PHP Ds\PriorityQueue::allocate() function is available in the Ds (Data Structures) extension for PHP which is used to allocate a specific capacity to a priority queue. This can improve performance by reducing the need to resize when objects are added.

Syntax

Below is the syntax of the PHP Ds\PriorityQueue::allocate() function −

public Ds\PriorityQueue::allocate(int $capacity): void

Parameters

This function accepts $capacity parameter which is an integral value that indicates how many values needs capacity to be allotted.

Return Value

This function does not return a value.

PHP Version

The allocate() function is available from version 1.0.0 of the Ds extension onwards.

Example 1

Here is the basic example of the PHP Ds\PriorityQueue::allocate() function to allocate a capacity of 10 to a priority queue.

<?php
   // Create a new PriorityQueue  
   $queue = new \Ds\PriorityQueue();

   //Use allocate function here
   $queue->allocate(10);

   //echo the message
   echo "Capacity allocated: 10\n";
?>

Output

Here is the outcome of the following code −

Capacity allocated: 10

Example 2

In the below PHP code we will try to use the allocate() function and we start adding elements to the queue after allocating space for five items.

<?php
   // Create a new PriorityQueue  
   $queue = new \Ds\PriorityQueue();

   // Use allocate function here
   $queue->allocate(5);
   
   $queue->push("A", 1);
   $queue->push("B", 2);
   $queue->push("C", 3);

   echo "The elements are:\n";
   
   foreach ($queue as $value) {
       echo $value . "\n";
   }
?> 

Output

This will generate the below output −

The elements are:
C
B
A

Example 3

Now the below code, we will check the capacity before and after allocation using allocate() function.

<?php
   // Create a new PriorityQueue  
   $queue = new \Ds\PriorityQueue();
   echo "Initial capacity: " . $queue->capacity() . "\n";
   
   $queue->allocate(20);
   echo "Capacity after allocation: " . $queue->capacity() . "\n";
?> 

Output

This will create the below output −

Initial capacity: 8
Capacity after allocation: 32

Example 4

In this example, a capacity is allocated initially using allocate() function, and additional elements are added until the capacity is exceeded.

<?php
   // Create a new PriorityQueue
   $queue = new \Ds\PriorityQueue();
   $queue->allocate(2);
   
   $queue->push("X", 1);
   $queue->push("Y", 2);
   $queue->push("Z", 3); // Exceeds initial allocation
   
   echo "After exceeding the initial allocation: \n";

   foreach ($queue as $value) {
       echo $value . "\n";
   }
?> 

Output

Following is the output of the above code −

After exceeding the initial allocation: 
Z
Y
X

Summary

The Ds\PriorityQueue allocate() function can ensure that enough memory is allocated for the required capacity. It can remove the need to reallocate internal as values are added.