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This example shows how to create an immutable lightweight class that serves only to encapsulate a set of auto-implemented properties. Use this kind of construct instead of a struct when you must use reference type semantics.
Note that with auto-implemented properties, both a get and set accessor are required. You make the class immutable by declaring the set accessors as private. However, when you declare a private set accessor, you cannot use an object initializer to initialize the property. You must use a constructor or a factory method.
Example
The following example shows two ways to implement an immutable class that has auto-implemented properties. The first class uses a constructor to initialize the properties, and the second class uses a static factory method.
// This class is immutable. After an object is created,
// it cannot be modified from outside the class. It uses a
// constructor to initialize its properties.
class Contact
{
// Read-only properties.
public string Name { get; private set; }
public string Address { get; private set; }
// Public constructor.
public Contact(string contactName, string contactAddress)
{
Name = contactName;
Address = contactAddress;
}
}
// This class is immutable. After an object is created,
// it cannot be modified from outside the class. It uses a
// static method and private constructor to initialize its properties.
public class Contact2
{
// Read-only properties.
public string Name { get; private set; }
public string Address { get; private set; }
// Private constructor.
private Contact2(string contactName, string contactAddress)
{
Name = contactName;
Address = contactAddress;
}
// Public factory method.
public static Contact2 CreateContact(string name, string address)
{
return new Contact2(name, address);
}
}
public class Program
{
static void Main()
{
// Some simple data sources.
string[] names = {"Terry Adams","Fadi Fakhouri", "Hanying Feng",
"Cesar Garcia", "Debra Garcia"};
string[] addresses = {"123 Main St.", "345 Cypress Ave.", "678 1st Ave",
"12 108th St.", "89 E. 42nd St."};
// Simple query to demonstrate object creation in select clause.
// Create Contact objects by using a constructor.
var query1 = from i in Enumerable.Range(0, 5)
select new Contact(names[i], addresses[i]);
// List elements cannot be modified by client code.
var list = query1.ToList();
foreach (var contact in list)
{
Console.WriteLine("{0}, {1}", contact.Name, contact.Address);
}
// Create Contact2 objects by using a static factory method.
var query2 = from i in Enumerable.Range(0, 5)
select Contact2.CreateContact(names[i], addresses[i]);
// Console output is identical to query1.
var list2 = query2.ToList();
// List elements cannot be modified by client code.
// CS0272:
// list2[0].Name = "Eugene Zabokritski";
// Keep the console open in debug mode.
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
/* Output:
Terry Adams, 123 Main St.
Fadi Fakhouri, 345 Cypress Ave.
Hanying Feng, 678 1st Ave
Cesar Garcia, 12 108th St.
Debra Garcia, 89 E. 42nd St.
*/
The compiler creates backing fields for each auto-implemented property. The fields are not accessible directly from source code.