Collections with SPL

Priority Queue

SplPriorityQueue extracts the item with the highest priority first.

priority order Priority queues use numeric priority instead of insertion order to choose the next item.

Priority Queue

urgent
priority_queue.php
Replay: real traced execution (multi-file project)
<?php
$urgent = 5;
$queue = new SplPriorityQueue();
$queue->insert("normal", 3);
$queue->insert("urgent", $urgent);
$picked = $queue->extract();
$left = $queue->count();

echo "urgent=" . $urgent . "\n";
echo "picked=" . $picked . "\n";
echo "left=" . $left . "\n";

<?php
$urgent = 1;
$queue = new SplPriorityQueue();
$queue->insert("normal", 3);
$queue->insert("urgent", $urgent);
$picked = $queue->extract();
$left = $queue->count();

echo "urgent=" . $urgent . "\n";
echo "picked=" . $picked . "\n";
echo "left=" . $left . "\n";

<?php
$urgent = 9;
$queue = new SplPriorityQueue();
$queue->insert("normal", 3);
$queue->insert("urgent", $urgent);
$picked = $queue->extract();
$left = $queue->count();

echo "urgent=" . $urgent . "\n";
echo "picked=" . $picked . "\n";
echo "left=" . $left . "\n";

  1. $urgent ← 5, $queue ← SplPriorityQueue, $picked ← urgent, $left ← 1

    1<?php2$urgent→ 5 = 5; //@urgent=1, 93$queue→ SplPriorityQueue = new SplPriorityQueue();4$queueSplPriorityQueue->insert("normal", 3);5$queueSplPriorityQueue->insert("urgent", $urgent5);6$picked→ urgent = $queueSplPriorityQueue->extract();7$left→ 1 = $queueSplPriorityQueue->count();89echo "urgent=" . $urgent5 . "\n";10echo "picked=" . $pickedurgent . "\n";11echo "left=" . $left1 . "\n";
    outputurgent=5
picked=urgent
left=1

  1. $urgent ← 1, $queue ← SplPriorityQueue, $picked ← normal, $left ← 1

    1<?php2$urgent→ 1 = 1;3$queue→ SplPriorityQueue = new SplPriorityQueue();4$queueSplPriorityQueue->insert("normal", 3);5$queueSplPriorityQueue->insert("urgent", $urgent1);6$picked→ normal = $queueSplPriorityQueue->extract();7$left→ 1 = $queueSplPriorityQueue->count();89echo "urgent=" . $urgent1 . "\n";10echo "picked=" . $pickednormal . "\n";11echo "left=" . $left1 . "\n";
    outputurgent=1
picked=normal
left=1

  1. $urgent ← 9, $queue ← SplPriorityQueue, $picked ← urgent, $left ← 1

    1<?php2$urgent→ 9 = 9;3$queue→ SplPriorityQueue = new SplPriorityQueue();4$queueSplPriorityQueue->insert("normal", 3);5$queueSplPriorityQueue->insert("urgent", $urgent9);6$picked→ urgent = $queueSplPriorityQueue->extract();7$left→ 1 = $queueSplPriorityQueue->count();89echo "urgent=" . $urgent9 . "\n";10echo "picked=" . $pickedurgent . "\n";11echo "left=" . $left1 . "\n";
    outputurgent=9
picked=urgent
left=1