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Introduction

Just about everything is a heap object when you are using C#. Only elementary native types like int are treated as value types. But there are two value types in C# that are pretty much more useful that first glances would tell you. They are the enum and struct types. Very few tutorials even cover these topics, but they have their own uses. And both of them are a lot more efficient than classes and you can use them in place of classes when they meet your requirements to improve performance.

Enums

Enums are basically a set of named constants. They are declared in C# using the enum keyword. Every enum type automatically derives from System.Enum and thus we can use System.Enum methods on our Enums. Enums are value types and are created on the stack and not on the heap. You don't have to use new to create an enum type. Declaring an enum is a little like setting the members of an array as shown below. 

enum Rating {Poor, Average, Okay, Good, Excellent}

You can pass enums to member functions just as if they were normal objects. And you can perform arithmetic on enums too. For example we can write two functions, one to increment our  enum and the other to decrement our enum.

Rating IncrementRating(Rating r)
{
    if(r == Rating.Excellent)
        return r;
    else
        return r+1;
}
Rating DecrementRating(Rating r)
{
    if(r == Rating.Poor)
        return r;
    else
        return r-1;
}

Both functions take a Rating object as argument and return back a Rating object. Now we can simply call these functions from elsewhere.

for (Rating r1 = Rating.Poor; 
    r1 < Rating.Excellent ; 
    r1 = IncrementRating(r1))
{           
    Console.WriteLine(r1);
}

Console.WriteLine();

for (Rating r2 = Rating.Excellent; 
    r2 > Rating.Poor; 
    r2 = DecrementRating(r2))
{
    Console.WriteLine(r2);          
}

And here is a sample code snippet showing how you can call System.Enum methods on our Enum object. We call the GetNames method which retrieves an array of the names of the constants in the enumeration.

foreach(string s in Rating.GetNames(typeof(Rating)))
    Console.WriteLine(s);

Where to use enums

Quite often we have situations where a class method takes as an argument a custom option. Let's say we have some kind of file access class and there is a file open method that has a parameter that might be one of read-mode, write-mode, read-write-mode, create-mode and append-mode. Now you might think of adding five static member fields to your class for these modes. Wrong approach! Declare and use an enumeration which is a whole lot more efficient and is better programming practice in my opinion.

Structs

In C++ a struct is just about the same as a class for all purposes except in the default access modifier for methods. In C# a struct are a pale puny version of a class. I am not sure why this was done so, but perhaps they decided to have a clear distinction between structs and classes. Here are some of the drastic areas where classes and structs differ in functionality.

struct Student : IGrade
{   
    public int maths;
    public int english;
    public int csharp;

    //public member function

    public int GetTot()
    {
        return maths+english+csharp;
    }

    //We have a constructor that takes an int as argument

    public Student(int y)
    {
        maths = english = csharp = y;
    }

    //This method is implemented because we derive

    //from the IGrade interface

    public string GetGrade()
    {
        if(GetTot() > 240 )
            return "Brilliant";
        if(GetTot() > 140 )
            return "Passed";
        return "Failed";
    }
}

interface IGrade
{
    string GetGrade();
}

Well, now let's take a look at how we can use our struct.

Student s1 = new Student();
Console.WriteLine(s1.GetTot());
Console.WriteLine(s1.GetGrade());

//Output

0
Failed

Here the default constructor gets called. This is automatically implemented for us and we cannot have our own default parameter-less constructor. The default parameter-less constructor simply initializes all values to their zero-equivalents. This is why we get a 0 as the total.

Student s2;
s2.maths = s2.english = s2.csharp = 50;
Console.WriteLine(s2.GetTot());
Console.WriteLine(s2.GetGrade());

//Output

150
Passed

Because we haven't used new, the constructor does not get called. Of all the silly features this one must win the annual contest by a long way. I see no sane reason why this must be so. Anyway you have to initialize all the member fields. If you comment out the line that does the initialization you will get a compiler error :- Use of unassigned local variable 's2'

Student s3 = new Student(90);
Console.WriteLine(s3.GetTot());
Console.WriteLine(s3.GetGrade());

//Output

270
Brilliant

This time we use our custom constructor that takes an int as argument.

When to use structs

Because structs are value types they would be easier to handle and more efficient that classes. When you find that you are using a class mostly for storing a set of values, you must replace those classes with structs. When you declare arrays of structs because they are created on the heap, efficiency again improves. Because if they were classes each class object would need to have memory allocated on the heap and their references would be stored. In fact lots of classes within the .NET framework are actually structs. For example System.Drawing.Point is actually a struct and not a class.

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QuestionProblem of Event and Delegate Pin
sanjayror		9:00 25 Oct '08  
GeneralNewbie Question Pin
akobold		3:15 31 Jan '07  
AnswerRe: Newbie Question Pin
Kevinyou		6:45 26 May '07  
GeneralHow to load a lot of data into structs? Pin
Brent_Daignault		12:11 14 Oct '05  
GeneralProblems with structs in C# Pin
ghost1207		1:11 7 Feb '05  
GeneralRe: Problems with structs in C# Pin
Anonymous		7:49 9 Mar '05  
GeneralRe: Problems with structs in C# Pin
kam18		10:28 14 Aug '06  
GeneralUsing typedef structs in C# ,C++ Pin
arssa2020		10:26 17 Jun '04  
GeneralDoes know anybody how to extend a enum? Pin
srlopez		5:21 25 Feb '03  
GeneralRe: Does know anybody how to extend a enum? Pin
Daniel Turini		5:32 25 Feb '03  
GeneralRe: Does know anybody how to extend a enum? Pin
srlopez		5:40 25 Feb '03  
GeneralRe: Does know anybody how to extend a enum? Pin
Daniel Turini		5:42 25 Feb '03  
GeneralRe: Does know anybody how to extend a enum? Pin
doohickeywannabeewannabe		12:58 26 Nov '06  
GeneralRe: Does know anybody how to extend a enum? Pin
Kevinyou		7:23 26 May '07  
GeneralLanguage bug or language feature? Pin
dcbrower		5:26 8 Jan '03  
GeneralGuess: why no overloading default struct ctor Pin
willtsmith		21:08 4 Jan '03  
GeneralYou rock Nish Pin
Paul Watson		8:57 4 Nov '02  
GeneralRe: You rock Nish Pin
Nishant S		15:18 4 Nov '02  
GeneralRe: You rock Nish Pin
Paul Watson		20:13 5 Nov '02  
GeneralBest practice of using enums and a data source Pin
Paul Watson		6:18 17 Oct '02  
GeneralRe: Best practice of using enums and a data source Pin
Nishant S		6:58 17 Oct '02  
GeneralRe: Best practice of using enums and a data source Pin
Paul Watson		7:13 17 Oct '02  
GeneralRe: Best practice of using enums and a data source Pin
James T. Johnson		15:40 17 Oct '02  
GeneralRe: Best practice of using enums and a data source Pin
Nishant S		16:27 17 Oct '02  
GeneralRe: Best practice of using enums and a data source Pin
James T. Johnson		16:54 17 Oct '02  
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