Implementing a conditional in a free interface

Question

I am trying to implement a free interface for a set of rules in my system. What I'm trying to accomplish is

TicketRules .RequireValidation() .When(quartType => quartType == QuartType.Before).TotalMilageIs(64) .When(quartType => quartType == QuartType.After).TotalMilageIs(128); 

However, I am having problems implementing When when condition, which I actually was. Currently I need to call When () twice, as in this snippet:

 rules.When(param => param.Remarque == "Test").TotalMilageIs(100); rules.When(param => param.Remarque == "Other").TotalMilageIs(50); var params1 = new AddTicketParameters() { Remarque = "Test" }; var params2 = new AddTicketParameters() { Remarque = "Other" }; rules.ExecuteWith(params1); Assert.That(ticket.TotalMilage, Is.EqualTo(100)); rules.ExecuteWith(params2); Assert.That(ticket.TotalMilage, Is.EqualTo(50)); 

The TicketRules class is as follows:

 [EditorBrowsable(EditorBrowsableState.Never)] public class TicketRules : ITicketRule, IHideObjectMembers { private Ticket theTicket; public Ticket Ticket { set { theTicket = value; } } private List<ITicketRule> allRules = new List<ITicketRule>(); public TicketRules() { } public TicketRules(Ticket ticket) { theTicket = ticket; } public void Execute() { ExecuteWith(null, null); } public void ExecuteWith(AddTicketParameters param) { ExecuteWith(param, null); } public virtual void ExecuteWith(AddTicketParameters param, Ticket outsideTicket) { foreach (ITicketRule rule in allRules) { rule.ExecuteWith(param, theTicket ?? outsideTicket); } } public TicketRules RequireValidation() { CreateModifierRule(ticket => ticket.NeedValidation = true); return this; } public TicketRules TotalMilageIs(int milage) { CreateModifierRule(ticket => ticket.TotalMilage = milage); return this; } private void CreateModifierRule(Action<Ticket> function) { AddRule(new ModifierTicketRule(function)); } internal void AddRule(ITicketRule rule) { allRules.Add(rule); } public WhenClauseTicketRule When(Predicate<AddTicketParameters> predicate) { WhenClauseTicketRule whenClause = new WhenClauseTicketRule(); whenClause.Predicate = predicate; AddRule(whenClause); return whenClause; } public TicketRules UseStandardFormulaForTotalMilageAndTime() { AddRule(new StandardFormulaTicketRule()); return this; } public TicketRules EnsureMinimumMilageIs(int milage) { AddRule(new EnsureMinimumMilageTicketRule(milage)); return this; } } 

ITicketRules

 internal interface ITicketRule : IHideObjectMembers { void ExecuteWith(AddTicketParameters param, Ticket ticket); } 

I also need to support subclasses of AddTicketParameters in the When clause (maybe I'm using generics for this part). I post here because everything confuses me in my design, and Martin Fowler 's articles confuse me even more.

Answer 1

This is called a termination problem when the method chain try this

 TicketRules .RequireValidation() .When(quartType => quartType == QuartType.Before, rule => rule.TotalMilageIs(64)) .When(quartType => quartType == QuartType.After, rule => rule.TotalMilageIs(128)); 

It looks a little strange at first, but it takes your conditional expressions to another area, so you can conditionally execute them. Think of it as creating your own if block. By closing it, you know when you can “finish” the subtitle.