I got tripped up by the following code:
// This data actually comes from csv file
$data = array(
array('Area1', null, null),
array(null, 'Section1', null),
array(null, null, 'Location1'),
array('Area2', null, null),
array(null, 'Section2', null),
array(null, null, 'Location2')
);
$root = array();
foreach ($data as $row) {
if ($row[0]) { // Is Area
$area = array();
$root[$row[0]] =& $area;
} elseif ($row[1]) { // Is Section
$section = array();
$area[$row[1]] =& $section;
} elseif ($row[2]) { // Is Location
$section[] = $row[2];
}
}
print_r($root);
Expected result:
Array(
[Area1] => Array(
[Section1] => Array(
[0] => Location1
)
)
[Area2] => Array(
[Section2] => Array(
[0] => Location2
)
)
)
Actual result:
Array(
[Area1] => Array(
[Section2] => Array(
[0] => Location2
)
)
[Area2] => Array(
[Section2] => Array(
[0] => Location2
)
)
)
So what did I do wrong? To answer this lets look at a simpler example:
$a = array();
$b =& $a;
$a[] = 'hello';
echo implode(' ', $b); // Outputs 'hello'
$a = array('world');
echo implode(' ', $b); // Outputs 'world'
See I was expecting the last line to output 'hello' because I was thinking references were like C pointers. That is:
void* a = array();
void* b = *a;
So looking up the PHP manual it says:
They are not like C pointers; instead, they are symbol table aliases...
References can be thought of as hardlinking in Unix filesystem.
