在c#3.0中,是否可以在字符串类中添加隐式运算符？

public static class StringExtensions
{
    public static bool IsNullOrEmpty(this string str)
    {
        return string.IsNullOrEmpty(str);
    }
}

string myString = null;
if (myString.IsNullOrEmpty())
{
    Console.WriteLine("The string is null or empty.");
}

public class CustomString
{
    private string _value;

    public CustomString(string value)
    {
        _value = value;
    }

    public static implicit operator CustomString(string value)
    {
        return new CustomString(value);
    }

    public static implicit operator string(CustomString customString)
    {
        return customString._value;
    }
}