Understanding Arrays as part of the foreach in php

Having:

$a as $key => $value;

is the same as having:

$a=array()开发者_StackOverflow;

?

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

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.

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').

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);