Added Iterator example, slightly modified to better show the workings

examples-per-language/php/behavioral/Iterator.php

@@ -0,0 +1,32 @@
+<?php
+
+use designPatternsForHumans\behavioral\Iterator\RadioStation;
+use designPatternsForHumans\behavioral\Iterator\StationList;
+
+require_once __DIR__ . '/autoload.php';
+
+$stationList = new StationList();
+
+$stationList->addStation(new RadioStation(89));
+$stationList->addStation(new RadioStation(101));
+$stationList->addStation(new RadioStation(102));
+$stationList->addStation(new RadioStation(103.2));
+
+/** @var RadioStation $station */
+echo 'These are the known Radio Stations' . PHP_EOL;
+foreach ($stationList as $station) {
+    echo $station->getFrequency(). PHP_EOL;
+}
+
+$stationList->removeStation(new RadioStation(89));
+
+// To prove the station was indeed removed, we iterate through the list again.
+// Small caveat : Iterators need to be rewinded after beeing Iterated!
+$stationList->rewind();
+
+/** @var RadioStation $station */
+echo 'These are the known Radio Stations' . PHP_EOL;
+foreach ($stationList as $station) {
+    echo $station->getFrequency(). PHP_EOL;
+}
+

examples-per-language/php/behavioral/src/Iterator/RadioStation.php

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+<?php
+
+namespace designPatternsForHumans\behavioral\Iterator;
+
+
+class RadioStation
+{
+    protected $frequency;
+
+    public function __construct($frequency)
+    {
+        $this->frequency = $frequency;
+    }
+
+    public function getFrequency()
+    {
+        return $this->frequency;
+    }
+}

examples-per-language/php/behavioral/src/Iterator/StationList.php

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+<?php
+
+namespace designPatternsForHumans\behavioral\Iterator;
+
+use Countable;
+use Iterator;
+
+class StationList implements Countable, Iterator
+{
+
+    protected $stations = [];
+    protected $counter;
+
+    public function addStation(RadioStation $station)
+    {
+        $this->stations[] = $station;
+    }
+
+    public function removeStation(RadioStation $toRemove)
+    {
+        $toRemoveFrequency = $toRemove->getFrequency();
+        $this->stations = array_filter($this->stations, function (RadioStation $station) use ($toRemoveFrequency) {
+            return $station->getFrequency() !== $toRemoveFrequency;
+        });
+    }
+
+    public function current()
+    {
+        return $this->stations[$this->counter];
+    }
+
+    public function next()
+    {
+        $this->counter++;
+    }
+
+    public function key()
+    {
+        return $this->counter;
+    }
+
+    public function valid()
+    {
+        return isset($this->stations[$this->counter]);
+    }
+
+    public function rewind()
+    {
+        // When using a numbered array like we do with $counter, we need to reset
+        // the array as well, otherwise the removed station will wreak havoc with
+        // our iteration, because the value ox removed station at position X will
+        // be NULL;
+        $this->stations = array_values($this->stations);
+        return $this->counter = 0;
+    }
+
+    public function count()
+    {
+        return count($this->stations);
+    }
+}