Static Dictionary

A static Dictionary can store global data. It lets you quickly look up strings (or other values). It is shared among many instances.

A static Dictionary, existing only once in memory, is efficient. We can store values in one location, and access them from many methods.

Simple example

Let us begin with a simple example that shows the mechanics of using a static Dictionary. We can access the static "gems" dictionary in both Main, and the Test() method.

using System;
using System.Collections.Generic;

class Program
{
    static Dictionary<string, int> _gems = new Dictionary<string, int>();

    static void Main()
    {
        // Add some data to static dictionary.
        _gems.Add("diamond", 500);
        _gems.Add("ruby", 200);

        // Call another method.
        Test();
    }

    static void Test()
    {
        // Use static dictionary.
        _gems.TryGetValue("diamond", out int value);
        Console.WriteLine("STATIC DICTIONARY RESULT: {0}", value);
    }
}
STATIC DICTIONARY RESULT: 500

Complex example

The example here is useful code for finding a plural version of a word. You can pass in a string, and the method will return the pluralized version.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Write plural words from static Dictionary.
        var result = PluralStatic.GetPlural("game");
        Console.WriteLine("RESULT: {0}", result);
    }
}

/// <summary>
/// Contains plural logic in static class [separate file]
/// </summary>
static class PluralStatic
{
    /// <summary>
    /// Static string Dictionary example
    /// </summary>
    static Dictionary<string, string> _dict = new Dictionary<string, string>
    {
        {"entry", "entries"},
        {"image", "images"},
        {"view", "views"},
        {"file", "files"},
        {"result", "results"},
        {"word", "words"},
        {"definition", "definitions"},
        {"item", "items"},
        {"megabyte", "megabytes"},
        {"game", "games"}
    };

    /// <summary>
    /// Access the Dictionary from external sources
    /// </summary>
    public static string GetPlural(string word)
    {
        // Get the result from the static Dictionary.
        string result;
        if (_dict.TryGetValue(word, out result))
        {
            return result;
        }
        else
        {
            return null;
        }
    }
}
RESULT: games

Notes, storage

A static Dictionary can be stored in a non-static class. In this case, it will still be tied to the type, not the instance. A static Dictionary can improve performance.

Static Dictionaries can store global program data. We saw example code that encapsulates a static Dictionary in a class, which is instantiated only once in the entire program.