IDictionary

How can we use the C# IDictionary interface? Many lookup types (Dictionary, SortedDictionary) implement the IDictionary interface.

We can make types that implement IDictionary. But it is useful too as an abstraction—we can accept IDictionary as a parameter type.

Example

This program uses Dictionary and SortedDictionary. Suppose that you want to add some functionality that can work on an instance of Dictionary or an instance of SortedDictionary.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Dictionary implements IDictionary.
        Dictionary<string, string> dict = new Dictionary<string, string>();
        dict["A"] = "B";
        WriteKeyA(dict);

        // SortedDictionary implements IDictionary.
        SortedDictionary<string, string> sort = new SortedDictionary<string, string>();
        sort["A"] = "C";
        WriteKeyA(sort);
    }

    static void WriteKeyA(IDictionary<string, string> i)
    {
        // Use instance through IDictionary interface.
        Console.WriteLine(i["A"]);
    }
}
B
C

Fields and variables

It is also possible to have fields of type IDictionary. This can make it possible to have a class that can use any dictionary type without worrying about which one it is.

Discussion

The IDictionary type has many required methods. The Dictionary type itself is good at what it does. An alternative implementation would not be of much use in most programs.

IDictionary can be used in an implementation of a custom dictionary. It can also be used in programs that act upon different dictionary types including Dictionary and SortedDictionary.