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This week I ran a half-day hands on games development session at the Progressive .Net Tutorials hosted by Skills Matter in London. I believe this was the last conference to be held in Goswell Road before the big move to an exciting new venue.

My session was on mobile games development with F# as the implementation language:

Here’s a quick peek inside the room:

The session tasks were around 2 themes:

  • implement a times table question and answer game (think Nintendo’s Brain Training game)
  • extended a simple Flappy Bird clone

Times table game

The motivation behind this example was to help people:

  • build a simple game loop
  • pick up some basic F# skills

The first tasks , like asking a multiplication question, could be built using F#’s REPL (F# Interactive) and later tasks that took user input required running as a console application.

Here’s some of the great solutions that were posted up to F# Snippets:

To run them, create a new F# Console Application project in Xamarin Studio or Visual Studio and paste in the code (use the Raw view in F# Snippets to copy the code).

Dominic Finn’s source code includes some fun ASCII art too:

// _____ _   _ _____ _____ _____  ______  _  _   _____  _____ _     
//|  __ \ | | |  ___/  ___/  ___| |  ___|| || |_|  _  ||  _  | |    
//| |  \/ | | | |__ \ `--.\ `--.  | |_ |_  __  _| | | || | | | |    
//| | __| | | |  __| `--. \`--. \ |  _| _| || |_| | | || | | | |    
//| |_\ \ |_| | |___/\__/ /\__/ / | |  |_  __  _\ \_/ /\ \_/ / |____
// \____/\___/\____/\____/\____/  \_|    |_||_|  \___/  \___/\_____/

Flappy Bird clone

For this example I sketched out a flappy bird clone using Monogame (along with WinForms and WPF for comparison) with the idea that people could enhance and extend the game:


Monogame lets you target multiple platforms including iOS and Android along with Mac, Linux, Windows and even Rapsberry Pi!

The different flavours are available on F# Snippets, simply cut and paste them into an F# script file to run them:

All the samples and tasks are also available in a zip:

Have fun!

Has C# Peaked?

Microsoft’s C# programming language first appeared in 2000, over 15 years ago, that’s a long time in tech.

Every month or so there’s a “Leaving .Net” articles, the last one I bumped into was “The collapse of the .net ecosystem” from Justin Angel:

The article shows, through a series of charts, the level of interest in C# peaking and then falling.

This is what I’d consider to be the natural continuum of things, where languages have their day, and then slowly decline. In the past C was my primary language, then C++ and so on, why should C# be any different?

Disclaimer: This is not a leaving .Net post, just some of my own research that I thought I’d share, with a focus on the UK as that’s where I live.

Job trends provides statistics on job placements with specific keywords, lets look at C#:

csharp jobgraph

This chart appears to show job adverts peaking between around 2010 and 2012 and tapering off fairly heavily after that.

Google trends

Google trends lets you track interest over time based on a keyword, here I'm looking at C# in the UK:

On this chart the peak seems to be earlier, around 2009, perhaps the trend can be seen earlier in the UK, but again the decline in interest is clearly visible.


Questions around the validity of TIOBE’s numbers abound, but here it is anyway:

TIOBE Index for CSharp

Here the peak appears to be around 2012, although the drop is perhaps less pronounced.


Yet another popularity index this time tracking google trends for “C# tutorial” in the UK:


This chart shows uses a logarithmic scale, however what we might surmise, if the numbers are to believed, is that interest in C# appears to fall off a cliff towards the end of 2014.

Stack Overflow

The recent stackoverflow developer survey also shows a significant decline in interest from 44.7% in 2013 to 31.6% in 2015. Developer’s current preferences are also quite revealing:



Where’s everyone gone?

This is only conjecture, but from my experience of .Net oriented developer events over the years in the UK, C# has always had a significant focus on the web and ASP.Net. My suspicion is that with the rise of thick-client JavaScript and mobile, significant numbers of developers have been migrating naturally towards those ecosystems.

Should I panic?

Probably not, there’s still plenty of C# jobs out there for now, and hell, some of the best paid jobs nowadays are for maintaining C++ and even COBOL systems. But if the numbers are anything to go by then we can say that C# interest has peaked.

That said who knows what the future will hold and perhaps like C++ there’ll be a renaissance in the future, although C++’s renaissance never really brought it back to the levels of it’s heady hey days.

Then again perhaps it’s more pragmatic not to dwell too heavily on the past, accept the numbers, and look to a new future. If you’re skills extend beyond one language then I guess you’ve probably got nothing to worry about, otherwise perhaps it’s time to pick up a new language and new paradigms.

And I’ll leave you with a question: Do you think you’ll be using the same programming language in 5 years time?

A Fistful of Dollars

Just over a week ago I took the Eurostar over to Paris for NCrafts, a conference bringing together over 300 software craftsmen and craftswomen:

The event was held in a crypt and featured a good number of F# sessions:

Mathias Brandewinder gave an excellent closing talk on The T in TDD : tests, types, tales.

 NCrafts 2015 - May 2015

In this live coding session, Mathias took the multi-currency money example from Kent Beck’s seminal Test-Driven Development by Example book. First implementing a dollars class in C# driven by a unit test for quick feedback and then contrasting it with a similar implementation in F# using the REPL for immediate feedback.

Unit Test

The system needs to be able to multiply a price in dollars by a number of shares, so that 5 USD * 2 = 10 USD:

public class Tests
   public void five_dollars_times_two_should_equal_ten_dollars()
      // arrange
      var five = new Dollars(5);
      // act
      var result = five.Times(2);
      // assert
      Assert.AreEqual(new Dollars(10), result);

C# Dollars

Based on the test an immutable dollars class can be implemented:

public class Dollars
   private readonly decimal _amount;

   public Dollars(decimal value)
      _amount = value;

   public decimal Amount
      get { return _amount; }  

   public Dollars Times(decimal multiplier)
      return new Dollars(this._amount * multiplier);

The code now compiles, but the test fails!

C# Equality

The test fails because in C# class types use reference equality, so we must override Equals:

public class Dollars
   private readonly decimal _amount;

   public Dollars(decimal value)
      _amount = value;

   public decimal Amount
      get { return _amount; }  

   public Dollars Times(decimal multiplier)
      return new Dollars(this._amount * multiplier);

   public override bool Equals(object obj)
      var that = obj as Dollars;
         that != null
         ? this.Amount == that.Amount
         : false;

Note: at this point FXCop will also recommend that we implement GetHashCode as we’ve implemented Equals.

F# Dollars

In F#, the simplest thing that could possibly work is a measure type which gives compile time type safety:

[<Measure>] type usd

5.0M<usd> * 2.0M = 10.0M<usd>

We can also test it immediately in F# Interactive as above, or alternatively write a unit test as below:

let [<Test>] ``5 USD * 2 = 10 USD`` () =
   Assert.AreEqual(10M<usd>, 5M<usd> * 2M)

Note: F# units of measure are erased at compile time meaning there’s no runtime performance penalty.

F# Money

For a report we’d probably want to encode money dynamically with a currency component. Below I’ve chosen an F# record type:

type Money = { Amount:decimal; Currency:string } with
   member this.Times(multiplier) = { this with Amount = this.Amount * multiplier }

let USD amount = { Amount=amount; Currency="USD" }

USD 10M = (USD 5M).Times(2M)

This succeeds immediately as F# implements equality (and GetHashCode) by default for us on record types.


As an aside, I find assertions over numerical types are more natural using the Unquote library which lets you assert equality using the equals operator, i.e.

let [<Test>] ``5 USD * 2 = 10 USD`` () =
   test <@ (USD 5M).Times(2M) = USD 10M @>


When writing code we may seek quick feedback on our first implementations. In C# we’d typically write reflection based unit tests to get early feedback, in F# we may use F# interactive first for immediate feedback and later promote useful tests to reflection based tests that run as part of our continuous build and may help find regressions.

Also in this scenario implementing types in F# required a lot less boilerplate than the equivalent C# code.