class CollectionValidator

class CollectionValidator extends ConstraintValidator {
    public function validate(mixed $value, Constraint $constraint) : void {
        if (!$constraint instanceof Collection) {
            throw new UnexpectedTypeException($constraint, Collection::class);
        }
        if (null === $value) {
            return;
        }
        if (!\is_array($value) && !($value instanceof \Traversable && $value instanceof \ArrayAccess)) {
            throw new UnexpectedValueException($value, 'array|(Traversable&ArrayAccess)');
        }
        // We need to keep the initialized context when CollectionValidator
        // calls itself recursively (Collection constraints can be nested).
        // Since the context of the validator is overwritten when initialize()
        // is called for the nested constraint, the outer validator is
        // acting on the wrong context when the nested validation terminates.
        //
        // A better solution - which should be approached in Symfony 3.0 - is to
        // remove the initialize() method and pass the context as last argument
        // to validate() instead.
        $context = $this->context;
        foreach ($constraint->fields as $field => $fieldConstraint) {
            // bug fix issue #2779
            $existsInArray = \is_array($value) && \array_key_exists($field, $value);
            $existsInArrayAccess = $value instanceof \ArrayAccess && $value->offsetExists($field);
            if ($existsInArray || $existsInArrayAccess) {
                if (\count($fieldConstraint->constraints) > 0) {
                    $context->getValidator()
                        ->inContext($context)
                        ->atPath('[' . $field . ']')
                        ->validate($value[$field], $fieldConstraint->constraints);
                }
            }
            elseif (!$fieldConstraint instanceof Optional && !$constraint->allowMissingFields) {
                $context->buildViolation($constraint->missingFieldsMessage)
                    ->atPath('[' . $field . ']')
                    ->setParameter('{{ field }}', $this->formatValue($field))
                    ->setInvalidValue(null)
                    ->setCode(Collection::MISSING_FIELD_ERROR)
                    ->addViolation();
            }
        }
        if (!$constraint->allowExtraFields) {
            foreach ($value as $field => $fieldValue) {
                if (!isset($constraint->fields[$field])) {
                    $context->buildViolation($constraint->extraFieldsMessage)
                        ->atPath('[' . $field . ']')
                        ->setParameter('{{ field }}', $this->formatValue($field))
                        ->setInvalidValue($fieldValue)
                        ->setCode(Collection::NO_SUCH_FIELD_ERROR)
                        ->addViolation();
                }
            }
        }
    }

}