<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Comparing generators with Iterator objects</title>
</head>
<body><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.generators.syntax.html">Generator syntax</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.references.html">References Explained</a></div>
<div class="up"><a href="language.generators.html">Generators</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div><hr /><div id="language.generators.comparison" class="sect1">
<h2 class="title">Comparing generators with <a href="class.iterator.html" class="classname">Iterator</a> objects</h2>
<p class="para">
The primary advantage of generators is their simplicity. Much less
boilerplate code has to be written compared to implementing an
<a href="class.iterator.html" class="classname">Iterator</a> class, and the code is generally much more
readable. For example, the following function and class are equivalent:
</p>
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">getLinesFromFile</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileName</span><span style="color: #007700">) {<br /> if (!</span><span style="color: #0000BB">$fileHandle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileName</span><span style="color: #007700">, </span><span style="color: #DD0000">'r'</span><span style="color: #007700">)) {<br /> return;<br /> }<br /> <br /> while (</span><span style="color: #0000BB">false </span><span style="color: #007700">!== </span><span style="color: #0000BB">$line </span><span style="color: #007700">= </span><span style="color: #0000BB">fgets</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileHandle</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">yield $line</span><span style="color: #007700">;<br /> }<br /> <br /> </span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileHandle</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #FF8000">// versus...<br /><br /></span><span style="color: #007700">class </span><span style="color: #0000BB">LineIterator </span><span style="color: #007700">implements </span><span style="color: #0000BB">Iterator </span><span style="color: #007700">{<br /> protected </span><span style="color: #0000BB">$fileHandle</span><span style="color: #007700">;<br /> <br /> protected </span><span style="color: #0000BB">$line</span><span style="color: #007700">;<br /> protected </span><span style="color: #0000BB">$i</span><span style="color: #007700">;<br /> <br /> public function </span><span style="color: #0000BB">__construct</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileName</span><span style="color: #007700">) {<br /> if (!</span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">fileHandle </span><span style="color: #007700">= </span><span style="color: #0000BB">fopen</span><span style="color: #007700">(</span><span style="color: #0000BB">$fileName</span><span style="color: #007700">, </span><span style="color: #DD0000">'r'</span><span style="color: #007700">)) {<br /> throw new </span><span style="color: #0000BB">RuntimeException</span><span style="color: #007700">(</span><span style="color: #DD0000">'Couldn\'t open file "' </span><span style="color: #007700">. </span><span style="color: #0000BB">$fileName </span><span style="color: #007700">. </span><span style="color: #DD0000">'"'</span><span style="color: #007700">);<br /> }<br /> }<br /> <br /> public function </span><span style="color: #0000BB">rewind</span><span style="color: #007700">() {<br /> </span><span style="color: #0000BB">fseek</span><span style="color: #007700">(</span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">fileHandle</span><span style="color: #007700">, </span><span style="color: #0000BB">0</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">line </span><span style="color: #007700">= </span><span style="color: #0000BB">fgets</span><span style="color: #007700">(</span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">fileHandle</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">i </span><span style="color: #007700">= </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br /> }<br /> <br /> public function </span><span style="color: #0000BB">valid</span><span style="color: #007700">() {<br /> return </span><span style="color: #0000BB">false </span><span style="color: #007700">!== </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">line</span><span style="color: #007700">;<br /> }<br /> <br /> public function </span><span style="color: #0000BB">current</span><span style="color: #007700">() {<br /> return </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">line</span><span style="color: #007700">;<br /> }<br /> <br /> public function </span><span style="color: #0000BB">key</span><span style="color: #007700">() {<br /> return </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">i</span><span style="color: #007700">;<br /> }<br /> <br /> public function </span><span style="color: #0000BB">next</span><span style="color: #007700">() {<br /> if (</span><span style="color: #0000BB">false </span><span style="color: #007700">!== </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">line</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">line </span><span style="color: #007700">= </span><span style="color: #0000BB">fgets</span><span style="color: #007700">(</span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">fileHandle</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">i</span><span style="color: #007700">++;<br /> }<br /> }<br /> <br /> public function </span><span style="color: #0000BB">__destruct</span><span style="color: #007700">() {<br /> </span><span style="color: #0000BB">fclose</span><span style="color: #007700">(</span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">fileHandle</span><span style="color: #007700">);<br /> }<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
This flexibility does come at a cost, however: generators are forward-only
iterators, and cannot be rewound once iteration has started. This also
means that the same generator can't be iterated over multiple times: the
generator will need to either be rebuilt by calling the generator function
again, or cloned via the
<a href="language.oop5.cloning.html" class="link">clone</a> keyword.
</p>
</div><hr /><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.generators.syntax.html">Generator syntax</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.references.html">References Explained</a></div>
<div class="up"><a href="language.generators.html">Generators</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>
