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POPHP 5: return by ref method produces unexpected results
 

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  1. POPHP 5: return by ref method produces unexpected results
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    <p>I created a simple class to manage a tree data structure which seemed to behave strangely (code to follow). When it became apparent that this was not a mistake by me I created a test case which produced equally puzzling behavior. This is the same in 5.3 and 5.4.</p> <p>This is my test case:</p> <pre><code>&lt;?php class testcaseA { public function __construct($one=0, $two=1, $three=2) { $this-&gt;obj = new testcaseB($one++, $three, $two); } public function &amp;get($what){ return $this-&gt;obj-&gt;get($what); } } class testcaseB { public function __construct($one, &amp;$two, &amp;$three) { $this-&gt;one=$one; $this-&gt;two=$two; $this-&gt;three=$three; echo "\$one={$one}"; } public function &amp;get($what){ echo "&lt;p&gt;You asked for $what. $what ain't no country I ever heard of.&lt;br /&gt;"; echo "Check: [{$this-&gt;one}], {$this-&gt;two}, {$this-&gt;three}. Is this thing on?&lt;/p&gt;"; $this-&gt;obj[$what] = new testcaseB($this-&gt;one++,$this-&gt;two,$this-&gt;three); return $this-&gt;obj[$what]; } } ini_set('display_errors',1); error_reporting(E_ALL); $bob = new testcaseA(); $bob-&gt;get("What")-&gt;get("Spam")-&gt;get("America"); $bob-&gt;get("What")-&gt;get("EU")-&gt;get("France"); echo "&lt;pre&gt;"; print_r($bob); </code></pre> <p>Now the output that I expected was to see the value for $one increment 1,2,3,1,2,3 and produce a tree shape.</p> <p>This is the output I actually got:</p> <pre><code>$one=0 You asked for What. What ain't no country I ever heard of. Check: [0], 2, 1. Is this thing on? $one=0 You asked for Spam. Spam ain't no country I ever heard of. Check: [0], 2, 1. Is this thing on? $one=0 You asked for America. America ain't no country I ever heard of. Check: [0], 2, 1. Is this thing on? $one=0 You asked for What. What ain't no country I ever heard of. Check: [1], 2, 1. Is this thing on? $one=1 You asked for EU. EU ain't no country I ever heard of. Check: [1], 2, 1. Is this thing on? $one=1 You asked for France. France ain't no country I ever heard of. Check: [1], 2, 1. Is this thing on? $one=1 testcaseA Object ( [obj] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [What] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [EU] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [France] =&gt; testcaseB Object ( [one] =&gt; 1 [two] =&gt; 2 [three] =&gt; 1 ) ) ) ) ) ) ) ) </code></pre> <p>This confused me at first but I wondered if maybe the chained usage was setting values in a way I was not expecting.</p> <p>So I tried this which I added after the previous code:</p> <pre><code>...same classes and initial code as before... $a=$bob-&gt;get("What"); $b=$a-&gt;get("Spam"); $c=$b-&gt;get("America"); //$bob-&gt;get("What") $d=$a-&gt;get("EU"); $e=$d-&gt;get("France"); print_r($bob); </code></pre> <p>This produced a different but still unpredictable set of results.</p> <pre><code>You asked for What. What ain't no country I ever heard of. Check: [2], 2, 1. Is this thing on? $one=2 You asked for Spam. Spam ain't no country I ever heard of. Check: [2], 2, 1. Is this thing on? $one=2 You asked for America. America ain't no country I ever heard of. Check: [2], 2, 1. Is this thing on? $one=2 You asked for EU. EU ain't no country I ever heard of. Check: [3], 2, 1. Is this thing on? $one=3 You asked for France. France ain't no country I ever heard of. Check: [3], 2, 1. Is this thing on? $one=3testcaseA Object ( [obj] =&gt; testcaseB Object ( [one] =&gt; 3 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [What] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [Spam] =&gt; testcaseB Object ( [one] =&gt; 3 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [America] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 ) ) ) [EU] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [France] =&gt; testcaseB Object ( [one] =&gt; 3 [two] =&gt; 2 [three] =&gt; 1 ) ) ) ) ) ) ) ) </code></pre> <p>This is still not the behavior that I am after but it is closer. What I need is to use a chain of objects to traverse the tree (as with the first case), a pointer to the values $two and $three which in the real case are arrays and not swapped about. What I don't want to do is copy objects needlessly.</p> <p>On the other hand I do need to have all the objects share a single pair of variables which they all use.</p> <p>My guess is that the method <code>get()</code> could afford to be <code>byval</code> rather than <code>byref</code> although instinctively this seems wrong. </p> <p>Can anyone explain what the <code>$one</code> value is doing?</p> <p>Also can anyone help me understand the behavior of the first test case especially to the values in the array the first time?</p> <p><strong>UPDATE</strong></p> <p>Making use of the awesome suggestions our test case now looks like:</p> <pre><code>class testcaseA { public function __construct($one=0, $two=1, $three=2) { $this-&gt;obj = new testcaseB(++$one, $three, $two); } public function &amp;get($what){ return $this-&gt;obj-&gt;get($what); } } class testcaseB { public function __construct($one, &amp;$two, &amp;$three) { $this-&gt;one=$one; $this-&gt;two=$two; $this-&gt;three=$three; echo "[New:\$one={$one}]:"; } //public function &amp;get($what){ public function &amp;get($what){ //echo "&lt;p&gt;You asked for $what. $what ain't no country I ever heard of.&lt;br /&gt;"; echo "Get:{$what}:[{$this-&gt;one}]&lt;br /&gt;"; if(!isset($this-&gt;obj[$what])){ $this-&gt;obj[$what] = new testcaseB(++$this-&gt;one,$this-&gt;two,$this-&gt;three); } return $this-&gt;obj[$what]; } } echo "STARTING:&lt;br /&gt;"; ini_set('display_errors',1); error_reporting(E_ALL); echo "REALLY STARTING:&lt;br /&gt;"; echo "&lt;pre&gt;"; echo "&lt;p&gt;One at a time:&lt;/p&gt;"; $bob = new testcaseA(); $a=$bob-&gt;get("What"); $b=$a-&gt;get("Spam"); $c=$b-&gt;get("America"); $d=$a-&gt;get("EU"); $e=$d-&gt;get("France"); echo "&lt;br /&gt;"; print_r($bob); echo "&lt;p&gt;Chained:&lt;/p&gt;"; $bobby = new testcaseA(); $bobby-&gt;get("What")-&gt;get("Spam")-&gt;get("America"); $bobby-&gt;get("What")-&gt;get("EU")-&gt;get("France"); echo "&lt;br /&gt;"; print_r($bob); </code></pre> <p>The out put of which is:</p> <pre><code>STARTING: REALLY STARTING: One at a time: [New:$one=1]:Get:What:[1] [New:$one=2]:Get:Spam:[2] [New:$one=3]:Get:America:[3] [New:$one=4]:Get:EU:[3] [New:$one=4]:Get:France:[4] [New:$one=5]: testcaseA Object ( [obj] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [What] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [Spam] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [America] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 ) ) ) [EU] =&gt; testcaseB Object ( [one] =&gt; 5 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [France] =&gt; testcaseB Object ( [one] =&gt; 5 [two] =&gt; 2 [three] =&gt; 1 ) ) ) ) ) ) ) ) Chained: [New:$one=1]:Get:What:[1] [New:$one=2]:Get:Spam:[2] [New:$one=3]:Get:America:[3] [New:$one=4]:Get:What:[2] Get:EU:[3] [New:$one=4]:Get:France:[4] [New:$one=5]: testcaseA Object ( [obj] =&gt; testcaseB Object ( [one] =&gt; 2 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [What] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [Spam] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [America] =&gt; testcaseB Object ( [one] =&gt; 4 [two] =&gt; 2 [three] =&gt; 1 ) ) ) [EU] =&gt; testcaseB Object ( [one] =&gt; 5 [two] =&gt; 2 [three] =&gt; 1 [obj] =&gt; Array ( [France] =&gt; testcaseB Object ( [one] =&gt; 5 [two] =&gt; 2 [three] =&gt; 1 ) ) ) ) ) ) ) ) </code></pre> <p>The output numbers seem right but the <code>$one</code> are off in the stack. </p>
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    1. USMatthew Brown aka Lord Matt
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    1. COInterestingly I do not get expected behavior when get becomes a normal byval function.
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    2. CORunning the two versions (one after another and chain) in the other order still has chain doing bad things to the stack of objects. And yes I have now been schooled in the fact that $i++ is not the same as ++$i.
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