src/Utils/Str.php
public static function underscore($value)
    {
        if (isset(self::$underscored[$value])) {
            return self::$underscored[$value];
        }

        return self::$underscored[$value] = str_replace('-', '_', self::decamelize($value));
    }
public static function underscore($value)
    {
        if (isset(self::$underscored[$value])) {
            return self::$underscored[$value];
        }

        return self::$underscored[$value] = str_replace('-', '_', self::decamelize($value));
    }
Converts a camel case or dasherized string into a lower cased and underscored string.

@param $value
@return string