Struct

Structs vs. Classes

Structs may seem similar to classes, but there are important differences that you should be aware of. First of all, classes are reference types and structs are value types. By using structs, you can create objects that behave like the built-in types and enjoy their benefits as well.

Heap or Stack?

When you call the New operator on a class, it will be allocated on the heap. However, when you instantiate a struct, it gets created on the stack. This will yield performance gains. Also, you will not be dealing with references to an instance of a struct as you would with classes. You will be working directly with the struct instance. Because of this, when passing a struct to a method, it's passed by value instead of as a reference.

Example

// struct1.cs
using System;
struct SimpleStruct
{
    private int xval;
    public int X
    {
        get 
        {
            return xval;
        }
        set 
        {
            if (value < 100)
                xval = value;
        }
    }
    public void DisplayX()
     {
       Console.WriteLine("The stored value is: {0}", xval);
    }
} 

class TestClass
{
    public static void Main()
    {
        SimpleStruct ss = new SimpleStruct();
        ss.X = 5;
        ss.DisplayX();
     }
}

Constructors and Inheritance

Structs can declare constructors, but they must take parameters. It is an error to declare a default (parameterless) constructor for a struct. Struct members cannot have initializers. A default constructor is always provided to initialize the struct members to their default values.

When you create a struct object using the New operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the New operator. If you do not use New, the fields will remain unassigned and the object cannot be used until all the fields are initialized.

There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class object. A struct can implement interfaces, and it does that exactly as classes do. Here's a code snippet of a struct implementing an interface:

interface IImage
{
    void Paint();
} 

struct Picture : IImage
{
    public void Paint()
    {
         // painting code goes here
    }
    private int x, y, z;  // other struct members
}

Tips:

No "new" keyword is used. It is used like a value type such as int.

With structs you avoid the overhead of objects in the C# language. You can combine multiple fields. This reduces memory pressure. And it improves performance if the stack is not overwhelmed.