PHP each and static array declaration

Question

So, I've written some rather convoluted 'functional' PHP code to perform folding on an array. Don't worry, I won't use it anywhere. The problem is, PHP's 'each' function only seems to go as far as the end of an array as it is statically (actually, see bottom) declared.

// declare some arrays to fold with
$six = array("_1_","_2_","_3_","_4_","_5_","_6_");

// note: $ns = range(0,100) won't work at all--lazy evaluation?
$ns = array(1,2,3,4,5,6,7,8);
$ns[8] = 9; // this item is included

// add ten more elements to $ns. each can't find these
for($i=0; $i<10; ++$i)
    $ns[] = $i;

// create a copy to see if it fixes 'each' problem
$ms = $ns;
$ms[0] = 3; // Just making sure it's actually a copy

$f   = function( $a, $b ) { return $a . $b; };
$pls = function( $a, $b ) { return $a + $b; };

function fold_tr( &$a, $f )
{
    $g = function ( $accum, &$a, $f ) use (&$g)
    {
        list($dummy,$n) = each($a);
        if($n)
        {
            return $g($f($accum,$n),$a,$f);
        }
        else
        {
            return $accum;
        }
    };
    reset($a);
    return $g( NULL, $a, $f );
}

echo "<p>".fold_tr( $six, $f  )."</p>"; // as expected: _1__2__3__4__5__6_
echo "<p>".fold_tr( $ns, $pls )."</p>"; // 45 = sum(1..9)
echo "<p>".fold_tr( $ms, $pls )."</p>"; // 47 = 3 + sum(2..9)

I honestly have no clue how each maintains its state; it seems vestigial at best, since there are better (non-magical) mechanisms in the language for iterating through a list, but does anyone know why it would register items added to an array using $a[$index] = value but not '$a[] = value`? Thanks in advance any insight on this behavior.

cmbuckley · Accepted Answer · 2012-10-17 23:21:13Z

2

Your loop is exiting early thanks to PHP's weak typing:

if($n)
{
    return $g($f($accum,$n),$a,$f);
}
else
{
    return $accum;
}

when $n is 0 (e.g. $ns[9]), the condition will fail and your loop will terminate. Fix with the following:

if($n !== null)

answered Oct 17, 2012 at 23:21

cmbuckley

43k10 gold badges83 silver badges95 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Nathan Andrew Mullenax Over a year ago

Doh! I wish I had realized that a few hours ago. Thanks!

Collectives™ on Stack Overflow

PHP each and static array declaration

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related