Common Type System—Indexer Properties

Visual C# Tutorials

.NET Framework Tutorials

Common Type System Type Systems Intro § Types and Objects § Type Unification § Reference, Value Types § Accessibility, Visibility § Type Members § Fields § Methods § Locals Overloading Argument Passing Style Pass-by-Value and Pass-by-Reference Output Parameters Managed Pointers Variable Argument Methods Methods, Subclassing Virtuals, Overriding New Slots Exception Handlers Constructors, Instantiation § Default Constructors Value Construction Constructor Chaining Field Initialization Type Initializers Unhandled Exceptions Properties § Indexers Mixed Mode Accessibility Events Operator Overloading Coercion Subclassing, Polymorphism Styles of Inheritance § Implementation Inheritance Interface Inheritance Abstract Classes Interfaces § Method Dispatch Multiple Inheritance Private Interface Inheritance Private Inheritance Accessibility Interface Reimplementation Abstract and Interface? Sealing Types and Methods Runtime Type Checking Namespaces: Organizing Types § Define a Namespace Namespace Resolution Special Types § Delegates § CTS Support Co- and Contravariance Anonymous Delegates Custom Attributes Enumerations § Flags-Style Limitations Helper Methods Generics § Further Reading §

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Indexer Properties

A special variant on properties called an indexer property may be supplied. Consider this example:

class Customer
{
   private Dictionary<int, Order> orders;
 
   public Order this[int id]
   {
      get { return orders[id]; }
      set { orders[id] = value; }
   }
}

This is essentially a default property for a type, indicated by the System.Reflection.DefaultMemberAttribute in the IL. This style of property enables callers to access your object using special syntax. For example, C# permits callers to use an array-like syntax for this:

Customer c = /*...*/;
Order o = c[10010];

Indexer properties are also special in that they can be overloaded through the parameters. You may also use multiple parameters for input.