Enhance Collection Validation with containsOneItem() Closure Support

Laravel improves collection validation by adding closure support to the containsOneItem() method, enabling developers to verify that exactly one item satisfies custom conditions rather than just checking collection size.

Previously, containsOneItem() could only determine if a collection contained exactly one item total. The enhanced method now accepts closures, allowing precise validation that exactly one item meets specific criteria:

$collection = collect([1, 2, 3]);
 
$collection->containsOneItem(fn($item) => $item === 2); // true
$collection->containsOneItem(fn($item) => $item > 1);   // false (2 and 3 match)

This enhancement proves particularly valuable in business rule validation scenarios:

class BusinessRuleValidator
{
    public function validateTeamStructure(Collection $members)
    {
        // Ensure exactly one team lead exists
        if (!$members->containsOneItem(fn($member) => $member->role === 'lead')) {
            throw new ValidationException('Exactly one team lead required');
        }
 
        // Ensure exactly one budget approver
        if (!$members->containsOneItem(fn($member) => $member->can_approve_budget)) {
            throw new ValidationException('Exactly one budget approver required');
        }
 
        return true;
    }
 
    public function validateInvoiceItems(Collection $items)
    {
        $validations = [
            'handling' => $items->containsOneItem(fn($item) => $item->type === 'handling'),
            'processing' => $items->containsOneItem(fn($item) => $item->type === 'processing'),
            'delivery' => $items->containsOneItem(fn($item) => $item->type === 'delivery')
        ];
 
        foreach ($validations as $type => $isValid) {
            if (!$isValid) {
                throw new ValidationException("Exactly one {$type} fee required");
            }
        }
 
        return $items;
    }
}

The enhanced containsOneItem() method provides precise collection validation by ensuring exactly one item meets specific conditions, making business rule enforcement more reliable and expressive.