find_by.php

<?php

// test data

class Foo
{
    private $a;

    public function __construct($a)
    {
        $this->a = (int) $a;
    }
    
    public function hasGreaterAThan(self $another)
    {
        return $this->a > $another->a;
    }
}

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


/**
 * Finds an item in a list via a comparison function
 * 
 * @param  array    $aList      the collection to examine
 * @param  callable $comparison should compare two arguments and return a bool
 * @return mixed
 */
$find_by = function(array $aList, callable $comparison) {
    $callback = function($carry, $item) use ($comparison) {
        return ($carry == null || $comparison($item, $carry)) ? $item : $carry;
    };
    return array_reduce($aList, $callback);
};

$greaterA = function(Foo $foo1, Foo $foo2) {
    return $foo1->hasGreaterAThan($foo2);
};

$lesserA = function(Foo $foo1, Foo $foo2) {
    return $foo2->hasGreaterAThan($foo1);
};


assert($find_by($list, $greaterA) === $foo2);
assert($find_by($list, $lesserA) === $foo3);