Anonymous Objects or Types (.NET 3.0+ )

Anonymous types.

- April 20, 2015

Rest of the Story:


  • an anonymous type declaration begins with the new keyword followed by a member-initializer list in braces {}
  • the compiler generates a new class definition that contains the properties specified in the new member-initializer list
  • all properties of an anonymous type are public and immutable * anonymous type properties are read-only (you cannot modify a properties value once the object is created)
  • each property's type is inferred from the values assigned to it
  • the compiler defines a ToString method that returns comma-separated list of property-name = value pairs
  • Equals method compares the properties of two or more anonymous types

Examples... //Create a 'person' object using an anonymous type

var bob = new { Name = "Bob", Age = 37 };

bob in this case is the anonymous type, and the types of the properties are inferred by the value assigned. //display information (note here however that the ToString is not required as a ToString method is automatically defined and is the anonymous type)

Console.WriteLine("Bob:" + bob.ToString());
//the ToString() method would output the following
Bob: { Name = Bob, Age = 37 }
var steve = new { Name = "Steve", Age = 36 };
//the compiler is able to recognize the anonymous type for bob and steve are identical and of the same class by the fact that the properties and types were identical for both bob and steve
//the anonymous type also creates an equals method that is capable of comparing all objects of this anonymous type (so name and age properties will be compared)

Console.WriteLine(bob.Equals(steve) ? "equal" : "not equal"));

The output from the is "not equal".