You may type-hint on variadic functions in PHP to enforce type on elements in the array

variadic-generics.php

<?php
class Foo {}

$f1 = new Foo();
$f2 = new Foo();

$bar = function (Foo ...$foo) {
    foreach ($foo as $f) {
        echo get_class($f) . "\n";
    }
};

$bar($f1, $f2);

// Foo
// Foo

$bar($f1, 'bar', $f2);

// PHP Fatal error:  Uncaught TypeError: Argument 2 passed to {closure}() must 
// be an instance of Foo, string given