Indexers in Interfaces
You can declare indexers in an interface. To do this, specify the get and/or set keyword, but replace the body of the get or set accessor with a semicolon. Any class or struct that implements the interface must implement the indexer accessors declared in the interface. For example:
interface IRawInt { bool this [ int index ] { get; set; } } struct RawInt : IRawInt { ... public bool this [ int index ] { get { ... } set { ... } } ... }
If you implement the interface indexer in a class, you can declare the indexer implementations as virtual. This allows further derived classes to override the get and set accessors. For example:
class RawInt : IRawInt { ... public virtual bool this [ int index ] { get { ... } set { ... } } ... }
You can also choose to implement an indexer by using the explicit interface implementation syntax covered in Chapter 12, “Working with Inheritance.” An explicit implementation of an indexer is non-public and non-virtual (and so cannot be overridden). For example:
struct RawInt : IRawInt { ... bool IRawInt.this [ int index ] { get { ... } set { ... } } ... }