I am learning PHP from O'reilly media book 'Programing PHP' and I stumbled upon this:
function add_up ($running_total, $current_value) {
$running_total += $current_value * $current_value;
return $running_total;
}
$numbers = array(2, 3, 5, 7);
$total = array_reduce($numbers, 'add_up');
echo $total;
The array_reduce( ) line makes these function calls:
add_up(2,3)
add_up(11,5)
add_up(36,7)
// $total is now 87
But when I calculate I get 85. I think it should write like this:
The array_reduce( ) line makes these function calls:
add_up (0,2);
add_up (4,3);
add_up (13,5);
add_up (38,7);
Because optional value $initial is by default set to NULL.
mixed array_reduce ( array $input , callable $function [, mixed $initial = NULL ] )
Can somebody with more knowledge explain to me, who is wrong and why?
It has been reported in the errata (though not confirmed). But since you're not the only one to notice, you are most likely correct.
{128} Section "Reducing an Array";
Reducing An Array - Example of function calls created by array_reduce();
The array reduce() line makes these function calls:
add_up(2,3)
add_up(13,5)
add_up(38,7)
The correct list of calls should be:
add_up(0,2) // This line is missing in the book
add_up(4,3) // This line is incorrect in the book
add_up(13,5)
add_up(38,7)
[129] first example;
the resulting calls of the second example of array_reduce() should be:
add_up(11, 2)
add_up(15, 3)
add_up(24, 5)
add_up(49, 7)