Anonymous functions, or lambda functions, are functions without a name.
To invoke them, we need to store them as variables.
$addTaxes = function (array &$book, $percentage) { $book['price'] += round($percentage * $book['price'], 2); };
This preceding anonymous function gets assigned to the variable $addTaxes.
<?php $addTaxes = function (array &$book, $percentage) { $book['price'] += round($percentage * $book['price'], 2); }; // w w w . j ava 2 s .co m $books = [ ['title' => '2018', 'price' => 8.15], ['title' => 'Java', 'price' => 12.00], ['title' => 'Javascript', 'price' => 3.55] ]; foreach ($books as $index => $book) { $addTaxes($book, $index, 0.16); } var_dump($books); ?>