shouldn't PHP array recursion throw an error?

Question

This is the test and the response I get. I think this could be problematic and should throw an error or a notice but I cannot understand why is tolerated.

<?php
    $test = array( 0 => 'test', 1=> &$test );
    var_dump( $test );

    // array(2) { [0]=> string(4) "test" [1]=> &array(2) { [0]=> string(4) "test" [1]=> &array(2) { [0]=> string(4) "test" [1]=> *RECURSION* } } }
?>

I’m rather surprised that you can reference $test in the same expression that defined $test. $test = array('test'); $test[]=&$test; is pretty clear. But yours … — Gumbo
– Gumbo, Commented Jan 14, 2010 at 15:45
This is not a real problem and I was surprised as well. I was just playing with arrays and hit a personal dilema. — Elzo Valugi
– Elzo Valugi, Commented Jan 14, 2010 at 15:53
@Gumbo PHP is weird. You can assign references before the value exists: $x =& $y; $y = 5; for example is valid, with $y having never been defined earlier. — Paul
– Paul, Commented Jul 23, 2013 at 23:39

aercolino · Accepted Answer · 2010-01-14 15:45:40Z

5

It is true recursion, and *RECURSION* is not a real error message. It's not problematic, because $test is not actively recurring, and in this case var_dump is smart enough to stop before exhausting memory.

answered Jan 14, 2010 at 15:45

aercolino

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pauljwilliams · Accepted Answer · 2010-01-14 15:27:52Z

1

I would guess that detecting such a loop is non-trivial, and would be immediately apparent at runtime if the behaviour was incorrect.

answered Jan 14, 2010 at 15:27

pauljwilliams

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Alix Axel · Accepted Answer · 2010-01-14 15:28:10Z

1

Why is it problematic? PHP is smart enough to identify that an array is being recursively called.

The same happens if you print_r($GLOBALS), I see no harm in this.

answered Jan 14, 2010 at 15:28

Alix Axel

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Andy E · Accepted Answer · 2010-01-14 15:28:21Z

1

You're setting a reference, that is, a pointer so there is no true recursion, no loop. So no, it shouldn't throw an error.

answered Jan 14, 2010 at 15:28

Andy E

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streetparade · Accepted Answer · 2010-01-14 15:40:03Z

0

Actualy the *RECURSION* message is a error message, which ends the script execution. Else it would execute it till the memory limit is reaced.

answered Jan 14, 2010 at 15:40

streetparade

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