Writing Fluent APIs in C#: Comparing Dates Fluently

Kent Beck tweeted: screencast of a simple example of a fluent api driven by tests from @jitterted http://bit.ly/cSqtJE.

Using VS 2010 RC, C# and .NET 4.0

Ted Young gives a nice introduction into building fluent APIs using Java. He returns an instance of a DateBuilder to manage the dates. The .NET example copies this and uses extension methods.

I used VS 2010’s generate stub tooling for creating methods and classes while following Ted using IntelliJ IDEA in his video.

using System;
  
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var somedate = new DateTime(2010, 1, 10);
            var otherDate = new DateTime(2010, 1, 31);
  
            System.Diagnostics.Debug.Assert(somedate.IsBefore(otherDate));
            System.Diagnostics.Debug.Assert(otherDate.IsBefore(somedate) == false);
  
            System.Diagnostics.Debug.Assert(Dates.Is(otherDate).OnOrAfter(somedate));
            System.Diagnostics.Debug.Assert(Dates.Is(somedate).OnOrAfter(otherDate) == false);
  
            System.Diagnostics.Debug.Assert(Dates.Is(somedate).OnOrBefore(otherDate));
            System.Diagnostics.Debug.Assert(Dates.Is(otherDate).OnOrBefore(somedate) == false);
  
            System.Diagnostics.Debug.Assert(Dates.Is(otherDate).On(otherDate));
            System.Diagnostics.Debug.Assert(Dates.Is(otherDate).On(somedate) == false);
  
            
  
        }
    }
  
    public static class Dates
    {
        public static bool IsBefore(this DateTime firstDateTime, DateTime otherDate)
        {
            return (firstDateTime <= otherDate) ? true : false;
        }
  
        public static bool IsAfter(this DateTime firstDateTime, DateTime otherDate)
        {
            return (firstDateTime >= otherDate) ? true : false;
        }
  
        public static DatesBuilder Is(DateTime firstDateTime)
        {
            return new DatesBuilder(firstDateTime);
        }
  
        public class DatesBuilder
        {
            private DateTime _firstDateTime;
  
            public DatesBuilder(DateTime firstDateTime)
            {
                this._firstDateTime = firstDateTime;
            }
  
            public bool OnOrAfter(DateTime otherDate)
            {
                return !_firstDateTime.IsBefore(otherDate);
            }
  
            public bool OnOrBefore(DateTime otherDate)
            {
                return !_firstDateTime.IsAfter(otherDate);
            }
  
            public bool On(DateTime otherDate)
            {
                return _firstDateTime.Equals(otherDate);
            }
        }
    }
}

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UPDATE: Writing Fluent APIs in C#: Comparing Dates Fluently: 03.07.10 at 3:17 pm

{ 4 comments… read them below or add one }

Prof. Roger Crawfis 03.01.10 at 2:14 pm: So, I looked at this and Ted’s original article (a link to that is here).

I do not see the point to the DateBuilder class here. Extension methods would be a better approach (IMHO) for all of the methods. There is no reason to have this class.

Roger
Nick Robinson 03.28.10 at 10:39 am: I quite like the idea of doing:

DateTime someTime = ….

if(someTime.IsAfter(otherTime)) …

Which does achieve Teds original objective of making the code/compare more readable. I think canonically smaller builder classes are used however, so that the syntax available as you move down the fluent language tree, are restricted/minimised. I can see ted is just following that approach. But I do prefer the code above.

Nick.
Doug Finke 03.28.10 at 6:21 pm: @Nick, here is an updated version using extension methods.
UPDATE: Writing Fluent APIs in C#: Comparing Dates Fluently
Rakesh 08.23.11 at 2:23 pm: This is a nice article on fluent apis..there’s a similar one at http://dotnetfluent.com/csharp/csharp-net-4-0/implementing-a-fluent-api-using-extension-methods-in-c-4-0/

It uses extension methods..