“Handler” pattern?

Question

I\'ve come across a design pattern that\'s been referred to as a \"Handler Pattern,\" but I can\'t find any real references to this pattern anywhere. It\'s basically just a

Answer 1

I think the goal of avoiding recompiles is much better served by a COM influenced design. What extra flexibility do you get from this:

IHandler UserHandler = ...;

Dictionary result = UserHandler.Handle(
    new Dictionary{
        { "Action", "AddUser" },
        { "UserName", "Joe Bloggs" },
        { "Age", "23" } });
NewUserId = Int.Parse(result["UserId"]);

over:

IUserHandler UserHandler = ...;

AddUserResult result = UserHandler.AddUser(new AddUserArgs {
    UserName = "Joe Bloggs",
    Age = 23 });
NewUserId = result.UserId;

when you can extend the actions, results, and arguments:

IUserHandler UserHandler = ...;

AddUserResult2 result = UserHandler.AddUser(new AddUserArgs2 {
    UserName = "Joe Bloggs",
    Age = 23,
    Password = "xyzzy" });
NewUserId = result.UserId;
SessionId = result.SessionId;

IUserHandler2 UserHandler2 = UserHandler as IUserHandler2;
if (UserHandler2 != null)
{
    LoginUserResult loginResult = UserHandler2.LoginUser(new LoginUserArgs {
        UserId = NewUserId,
        SessionId = SessionId,
        Password = "xyzzy" });
}