Structure

Description

Structure is a "type", similar to "class", which can contain fields, methods, parameterized constructors, properties, and events.

• The instance of structure is called as "structure instance" or "structure variable"; but not called as 'object'.

  • We can't create object for structure.
  • Objects can be created only based on 'class'.

• Structure instances are stored in 'stack'.

• Structure doesn't support 'user-defined parameter-less constructor' and also destructor.
• Structure can't inherit from other classes or structures.
• Structure can implement one or more interfaces.
• Structure doesn't support virtual and abstract methods.
• Structures are mainly meant for storing small amounts of data (one or very few values).
• Structures are faster than classes, as their instances are stored in 'stack'.
• Structures are value type but classes are reference type
• Will store in stack
• Is good for one or two fields
• Can inherit from interfaces but can't inherit from other classes or structures

struct StructureName {
    // Fields
    // Methods
    // Parameterized Constructors
    // Properties
    // Events
}

Example:

struct Student
{
    public int studentId;
    public string studentName;

    public string GetStudentName()
    {
        return studentName;
    }
}

Key Points

Property	Normal Class	Abstract Class	Interface	Sealed Class	Static Class	Structure
Can Inherit from Other Classes	Yes	Yes	No	Yes	No	No
Can Inherit from Other Interfaces	Yes	Yes	Yes	Yes	No	Yes
Can be Inherited	Yes	Yes	Yes	No	No	No
Can be Instantiated	Yes	No	No	Yes	No	Yes
Non-Static Fields	Yes	Yes	No	Yes	No	Yes
Non-Static Methods	Yes	Yes	No	Yes	No	Yes
Non-Static Constructors	Yes	Yes	No	Yes	No	Yes
Non-Static Properties	Yes	Yes	No	Yes	No	Yes
Non-Static Events	Yes	Yes	Yes	Yes	No	Yes
Non-Static Destructors	Yes	Yes	No	Yes	No	No
Constants	Yes	Yes	No	Yes	Yes	Yes
Static Fields	Yes	Yes	No	Yes	Yes	Yes
Static Methods	Yes	Yes	No	Yes	Yes	Yes
Static Constructors	Yes	Yes	No	Yes	Yes	Yes
Static Properties	Yes	Yes	No	Yes	Yes	Yes
Static Events	Yes	Yes	No	Yes	No	No
Virtual Methods	Yes	Yes	No	Yes	No	No
Abstract Methods	No	Yes	Yes	Yes	No	No
Non-Static Auto-Impl Properties	Yes	Yes	No	Yes	No	No
Non-Static Indexers	Yes	Yes	No	Yes	No	Yes

Structures vs Classes

Structures	Classes
Structures are "value-types".	Classes are "reference-types".
Structure instances (includes fields) are stored in stack. Structures doesn't require Heap.	Class instances (objects) are stored in Heap; Class reference variables are stored in stack.
Suitable to store small data (only one or two values).	Suitable to store large data (any no. of values).
Memory allocation and de-allocation is faster, in case of one or two values.	Memory allocation and de-allocation is a bit slower.
Structures doesn't support Parameter-less constructor.	Classes support Parameter-less Constructor.
Structures doesn't support inheritance (can't be parent or child).	Classes support Inheritance.
The "new" keyword just initializes all fields of the "structure instance".	The "new" keyword creates a new object.
Structures doesn't support abstract methods and virtual methods.	Classes support abstract methods and virtual methods.
Structures doesn't support destructors.	Classes support destructors.
Structures are internally derived from System.ValueType System.Object -> System.ValueType -> Structures.	Classes are internally and directly derived from System.Object System.Object -> Classes.
Structures doesn't support to initialize "non-static fields", in declaration.	Classes support to initialize "non-static fields", in declaration.
Structures doesn't support "protected" and "protected internal" access modifiers.	Classes support "protected" and "protected internal" access modifiers.
Structure instances doesn't support to assign "null".	Class's reference variables support to assign "null".

Constructor

C# provides a parameter-less constructor for every structure by default, which initializes all fields.

• You can also create one or more user-defined parameterized constructors in structure.
• Each parameterized constructor must initialize all fields; otherwise, it will be compile-time error.
• The “new” keyword used with structure doesn't create any object / allocate any memory in heap; It is just a syntax to call constructor of structure.

public StructureName( datatype parameter )
{
    field = parameter;
}

Info

بدون استفاده از constructor اصلا نیازی به instantiate کردن و استفاده از کلیدواژه new نیست، مثل زیر:

Structure1 structure1;

structure1.x = 10;
structure1.y = 20;

Readonly Structure

Use readonly structures in case of all of these:

• All fields are readonly.
• All properties have only 'get' accessors (readonly properties).
• There is a parameterized constructor that initializes all the fields.
• You don't want to allow changes to any field or property of the structure.
• Methods can read fields but can't modify them.

Example:

readonly struct Student
{
    public readonly int studentId;
    public string studentName { get; }

    public Student()
    {
        studentId = 1;
        studentName = "Scott";
    }
}