max($list, $function) in php

max.php

<?php

// test data

class Foo {
    private $a;
    private $b;

    function __construct($a, $b)
    {
        $this->a = $a;
        $this->b = $b;
    }

    public function getA() { return $this->a; }
    public function getB() { return $this->b; }
}

$list = [
    $foo1 = new Foo(2, "bar"),
    $foo2 = new Foo(5, "baz"),
    $foo3 = new Foo(1, "bam"),
];


// simple

$isGreater = function($carry, $item) {
    return is_null($carry) || $item->getA() > $carry->getA() ? $item : $carry;
};

$maxOfList = array_reduce($list, $isGreater);
assert($maxOfList === $foo2);


// reusable max() function

$max = function($list, callable $extract) {
    $compare = function($carry, $item) use($extract) {
        return is_null($carry) || $extract($item) > $extract($carry) ? $item : $carry;
    };
    return array_reduce($list, $compare);
};

$extractA = function($x) { return $x->getA();};
assert($max($list, $extractA) === $foo2);

Ok, in order to have a truly simple and reusable function, you want find_by, not max_by. See my fork.

class PupilService
{
    public function findOldestIn(array $aListOfPupils)
    {
        $pupilIsOlder = function(Pupil $pupilA, Pupil $pupilB) {
            return $pupilA->isOlderThan($pupilB);
        };
        return find_by($aListOfPupils, $pupilIsOlder);
    }
}

http://3v4l.org/6O94O