I have my custom data type as

public class AppIdentiy
{
    public string ID { get; set; }

    public static implicit operator AppIdentiy(string userID)
    {
        var result = new AppIdentiy()
        {
            ID = userID
        };
        return result;
    }

    public static implicit operator string(AppIdentiy identity)
    {
        if (identity is null)
            return string.Empty;
        else if (string.IsNullOrEmpty(identity.ID))
            return string.Empty;

        return identity.ID;
    }

    //public static string operator +(AppIdentiy a) => a.ID;

}

I am using this AppIdentiy like this for example

AppIdentiy myIdentity  = '[email protected]';

string email = myIdentity; //setting the variable email with the value '[email protected]'

string comment  = "this is user email address '" + myIdentity + "' generated by xyz app'; //this is not working, I am expecting here when I use '+' operator with my datatype its value should populate here like 

“this is user email address ‘[email protected]’ generated by xyz app”

I am not getting how to decorate the + operator overloading in my AppIdentiy class