respect-validation/library/Rules/In.php

<?php
namespace Respect\Validation\Rules;

class In extends AbstractRule
{
    public $haystack;
    public $compareIdentical;

    public function __construct($haystack, $compareIdentical = false)
    {
        $this->haystack = $haystack;
        $this->compareIdentical = $compareIdentical;
    }

    public function reportError($input, array $extraParams = array())
    {
        return parent::reportError($input, $extraParams);
    }

    public function validate($input)
    {
        if (is_array($this->haystack)) {
            return in_array($input, $this->haystack, $this->compareIdentical);
        }

        if (!is_string($this->haystack)) {
            return false;
        }

        $enc = mb_detect_encoding($input);

        if ($this->compareIdentical) {
            return mb_strpos($this->haystack, $input, 0, $enc) !== false;
        }

        return mb_stripos($this->haystack, $input, 0, $enc) !== false;
    }
}