cx-newsletter/converters/1-campaign_type_converter.php

<?php

namespace cx_newsletter;

class campaign_type_converter
extends enum_converter
implements enum_converter_interface {
    public function load_string(string $target) : self {
        $this->target = match ($target) {
            'SMS' => campaign_type::sms,
            'EMAIL' => campaign_type::email
        };

        return $this;
    }

    public function get_string() : string {
        return match ($this->target) {
            campaign_type::sms => 'SMS',
            campaign_type::email => 'EMAIL'
        };
    }
}