PHP Bug #55021 Investigation

gistfile1.php

<?php

/*
 * I looked into this for a bit and I must say I was a bit confused
 * until the answer smacked me in the face.
 * 
 * The 'fn3' isn't doing what you think it's doing.  Upon glancing at
 * the code it may appear that $this->a['first'] is having the value
 * 'foo' appended to it (which doesn't make sense because
 * $this->a['first'] is a string, not an array).
 *
 * What is actually happening (according to my tests on PHP 5.2.17) is
 * that $b[$k][] is being evaluated first and then the result is being
 * used at the property name, which explains the "Cannot use [] for
 * reading" error.
 * 
 * Assuming your test code was changed and $this->a['first'] was an
 * array, the "slightly more correct" way would be to call
 * $this->{$b}[$k][] which would evaluate to $this->a['first'][].
 *
 * In my opinion this should be classified as "not a bug". * I looked into this for a bit and I must say I was a bit confused
 * until the answer smacked me in the face.
 *
 * The 'fn3' isn't doing what you think it's doing.  Upon glancing at
 * the code it may appear that $this->a['first'] is having the value
 * 'foo' appended to it (which doesn't make sense because
 * $this->a['first'] is a string, not an array).
 *
 * What is actually happening (according to my tests on PHP 5.2.17) is
 * that $b[$k][] is being evaluated first and then the result is being
 * used at the property name, which explains the "Cannot use [] for
 * reading" error.
 *
 * Assuming your test code was changed and $this->a['first'] was an
 * array, the "slightly more correct" way would be to call
 * $this->{$b}[$k][] which would evaluate to $this->a['first'][].
 *
 * In my opinion this should be classified as "not a bug".

 */

function derp() {
    $herp = TRUE;
    return ($herp == TRUE) ? TRUE : FALSE;
}

derp();
exit();



class C
{
    public $a = array('first' => 'baz');

    /**
     * This case is most interesting, because as it run parse error
     * @note don't parse $this->$b
     */
    public function fn3($k)
    {
        $b = 'a';
        $this->{$b}[$k] = array();
        $this->{$b}[$k][] = 'foo'; ///BUG Error parse : PHP Fatal error:  Cannot use [] for reading in .... 
    }

    /**
     * Solution for fix fn3
     */
    public function fn4($k)
    {
        $b = 'a';
        $tmp =& $this->$b;
        $tmp[$k][] = 'foo';
    }
}

$obj = new C;

$obj->fn3('first');

var_export($obj);