Understanding Arrays as part of the foreach in php - php

Question

Having:
$a as $key => $value;
is the same as having:
$a=array();
?

Answer 1

No, it's not. It's more like
list($key, $value) = each($arr);
See the manual
foreach ($arr as $key => $value) {
echo "Key: $key; Value: $value<br />\n";
}
is identical to
$arr = array("one", "two", "three");
reset($arr);
while (list($key, $value) = each($arr)) {
echo "Key: $key; Value: $value<br />\n";
}
Also see
The while Control Structure
list — Assign variables as if they were an array
each — Return the current key and value pair from an array and advance the array cursor
reset — Set the internal pointer of an array to its first element

Answer 2

First of all it has to say
foreach($a as $key => $value)
Then, as far as I know,
foreach($a = array())
doesn't compile.
That said, if you foreach, you iterate through the elements of an array. With the 'as' keyword, you get pairs of key/value for each element, where $key would be the index by which you can get $value:
$value = $a[$key];
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edit:
In other programming languages it would spell something like
foreach($key => $value in $a)
or (C#)
foreach(KeyValuePair<type1, type2> kv in a)
which I think is more intuitive, but basically the same.

Answer 3

if you have the following:
$a = array('foo' => array('element1', 'element2'), 'bar' => array('sub1', 'sub2'));
if you use $a as $key=> $value in the foreach loop,
$key will be 'foo', and $value will be array('element1', 'element2') in the first iteration, in the second $key == 'bar' and $value == array('sub1', 'sub2').

Answer 4

If you loop over an array using foreach, the array is the first expression inside the parenthesis.
It can be a variable, like $a, or an array literal like array(1, 2, 3). The following loops are identical:
With an array literal:
foreach(array(1, 2, 3) as $number)
print($number);
With a variable:
$a = array(1, 2, 3);
foreach($a as $number)
print($number);