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Reducing Code Complexity on Switch-blocks

, 7 Oct 2008
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Using a Dictionary instead of a switch-case construction to reduce complexity and increase testability

Introduction

A switch-block becomes complex very easily. All code is placed in one method and parts of it are used multiple times. In a lot of cases, a switch-block is based on an enum. Next to that, it's not possible to use a fall-through in C#. The only way to go from case to case is the use of the goto statement, which isn't a good idea when reducing complexity. Although I've written the examples in C#, it wouldn't be hard to apply the principles to other languages.

A Solution

A nice solution to get rid of large switch constructions is the use of a Dictionary<enum,delegate>. This way every element of the enum can be attached to a method. It is possible to call the right method for every enum possible. Because every enum has its own method, it's very easy to use this construction in a testdriven environment. Another nice thing is that it's no problem to call one method from another. Let me explain a little further with an example and some pseudo code. Imagine a program that prepares food. This part contains the recipes.

Let us start with the following enum:

Enum food{
    Apple,
    ApplePie,
    AppleJuice,
    Pizza
}

It's not hard to imagine that all of the foods need a specific preparation, but that some actions need to be done for different foods, like peeling an apple or baking in the oven.

To add the preparations to the Dictionary<enum, delegate>, we first need to define a delegate method:

delegate bool Preperation();

Now we need to define the actual preparation methods for every item of the enum, making sure they're declared the same way as the delegate, thus the same parameters and return value. The method returns a boolean when preparation is successful.

In this example, the methods may look something like this:

bool PeelApple()
{
	// code to remove peel
	return true;
}
bool BakePie()
{
	PreheatOven(180.0);
	PeelApple();
	CreatePie();
	while(!doneBaking())
		Bake();
	return true;
}
bool MakeAppleJuice()
{
	PeelApple();
	Juicify();
	return true;
}
bool BakePizza()
{
	PreheatOven(160.0);
	CreatePizza();
	while(!doneBaking())
		Bake();
	return true;
}

Notice that BakePie() and MakeAppleJuice() both call the method PeelApple(). This is not possible in a switch – case constructor, unless you call the methods from each case.

Now all that's left is to create and initialize the Dictionary.

Dictionary<food, /> FoodPreperation;
..
FoodPreperation = new Dictionary<food, Preperation>();
FoodPreperation.add(food.Apple, new Preperation(PeelApple));
FoodPreperation.add(food.ApplePie, new Preperation(BakePie));
FoodPreperation.add(food.AppleJuice, new Preperation(MakeAppleJuice));
FoodPreperation.add(food.Pizza, new Preperation(BakePizza));

Calling the methods is done by:

food FoodOfChoice = food.ApplePie;
FoodPreperation[FoodOfChoice]();

In the last code snippet, the method that goes with food.ApplePie is executed.

History

  • 07 Oct 2008 - Initial upload

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Timmy Kokke
Software Developer (Senior) Centric Netherlands B.V.
Netherlands Netherlands
Microsoft MVP Client Dev . Founder of http://StoreAppsUG.nl, the Dutch Windows Store apps and Windows Phone apps usergroup. XAML / HTML5 developer. Writer. Composer. Musician.
 
Twitter
@Sorskoot
 
Awards / Honers
• October 2010,2011,2012,2013: Awarded Microsoft Expression Blend MVP
• June 2009: Second Place in the WinPHP challenge
• February 2009: Runner-up in de Mix09 10k Challenge
• June 2008: Winner of the Microsoft expression development contest at www.dekickoff.nl
 
Bio
I started programming around 1992, when my father had bought our first home computer. I used GWBasic at that time. After using QBasic and Pascal for a few years I started to learn C/C++ in 1996. I went to the ICT Academy in 1997 and finnished it in 2002. Until December 2007 I worked as a 3D specialist. Besides modelling I worked on different development projects like a 3D based Scheduler and different simultion tools in C# and Java. Though out the years I've gained much experience with ASP.NET, Silverlight, Windows Phone and WinRT.
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Comments and Discussions

 
GeneralMy vote of 5 PinmemberManuel_Perez_II26-Jul-11 21:02 
GeneralMy vote of 5 PinmemberEklavya Mirani17-Jul-11 2:58 
GeneralMy vote of 5 PinmemberSAKryukov30-Nov-10 8:14 
GeneralNice PinmemberThanos Papathanasiou8-Feb-10 3:05 
GeneralMore improvements PinmemberSAKryukov11-Jan-10 7:05 
GeneralQuite correct approach! Long switch statements are for loosers. PinmemberSAKryukov11-Jan-10 6:44 
Generalswitch PinmemberSlava Khristich6-Jan-09 6:30 
GeneralRe: switch PinmemberDonsw26-Jan-09 13:37 
GeneralSpeed of this versus switch-blocks Pinmemberwwahammy27-Oct-08 1:33 
GeneralRe: Speed of this versus switch-blocks PinmemberTimmy Kokke29-Oct-08 22:18 
GeneralRe: Speed of this versus switch-blocks PinmemberSAKryukov11-Jan-10 7:28 
GeneralThats a Good Solution ! PinmemberSamer Abu Rabie24-Oct-08 11:42 
GeneralGood One PinmemberSneha B Patel14-Oct-08 23:30 
GeneralI've done the same kind of thing but used reflection to build the dictionary... PinmemberMember 21876788-Oct-08 15:56 
GeneralRe: I've done the same kind of thing but used reflection to build the dictionary... PinmemberTimmy Kokke8-Oct-08 20:27 
GeneralRe: I've done the same kind of thing but used reflection to build the dictionary... PinmemberMember 218767810-Oct-08 13:36 
GeneralRe: I've done the same kind of thing but used reflection to build the dictionary... PinmemberMember 218767814-Oct-08 13:31 
Scott Hanselman just did a blog on using the T4 templating engine that comes in Visual Studio 2008:
http://www.hanselman.com/blog/T4TextTemplateTransformationToolkitCodeGenerationBestKeptVisualStudioSecret.aspx[^]
 
The examples he lists are probably better than I can do.
GeneralI've done this. PinmemberJamie Nordmeyer8-Oct-08 4:30 
GeneralRe: I've done this. PinmemberTimmy Kokke8-Oct-08 20:23 
GeneralRe: I've done this. PinmemberJamie Nordmeyer9-Oct-08 4:54 
GeneralRe: I've done this. PinmemberPalisade12-Jul-11 10:19 
GeneralNice idea PinmemberLeeland Clay8-Oct-08 3:05 
GeneralA design pattern alternative Pinmemberervegter8-Oct-08 2:10 
GeneralRe: A design pattern alternative PinmemberTimmy Kokke8-Oct-08 2:16 
GeneralRe: A design pattern alternative Pinmemberzenwalker19851-Oct-11 18:18 

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