c# immutable dictionary

C# Immutable Dictionary

In C#, an ImmutableDictionary<TKey, TValue> is a thread-safe, read-only collection that stores key-value pairs. Once created, its content cannot be modified directly. Instead, any "modification" operation, such as adding or removing an element, returns a new instance, leaving the original collection unchanged. This makes it a valuable tool for applications requiring data integrity and thread safety.

Key Benefits of ImmutableDictionary

• Thread Safety: Immutable collections prevent race conditions because they cannot be altered once created.
• Predictable State: Any function or method using immutable dictionaries has predictable results, as the collection's state is consistent.
• Efficient Changes: Returns new dictionaries with changes applied, sharing unchanged data efficiently.

Creating and Using ImmutableDictionary

Example: Adding and Modifying Key-Value Pairs

Here's how to create and modify an immutable dictionary in C#:

using System;
using System.Collections.Immutable;

public class ImmutableDictionaryExample
{
    public static void Main()
    {
        // Create an immutable dictionary
        var capitals = ImmutableDictionary<string, string>.Empty
            .Add("USA", "Washington, D.C.")
            .Add("UK", "London")
            .Add("France", "Paris");

        // Add a new key-value pair, returns a new dictionary
        var updatedCapitals = capitals.Add("Germany", "Berlin");

        // Modify an existing value, returns a new dictionary
        var modifiedCapitals = updatedCapitals.SetItem("UK", "Edinburgh");

        Console.WriteLine("Original Dictionary:");
        foreach (var entry in capitals)
        {
            Console.WriteLine($"{entry.Key}: {entry.Value}");
        }

        Console.WriteLine("\nUpdated Dictionary (Added Germany):");
        foreach (var entry in updatedCapitals)
        {
            Console.WriteLine($"{entry.Key}: {entry.Value}");
        }

        Console.WriteLine("\nModified Dictionary (Changed UK):");
        foreach (var entry in modifiedCapitals)
        {
            Console.WriteLine($"{entry.Key}: {entry.Value}");
        }
    }
}

Other Common Operations

1. Remove: Removes a key-value pair, returning a new dictionary.
2. TryGetValue: Attempts to retrieve a value without exceptions.
3. ContainsKey: Checks if a key exists in the dictionary.
4. SetItems: Adds or updates multiple key-value pairs at once.

Best Practices for ImmutableDictionary

• Avoid Frequent Copies: Minimize intermediate copies when chaining multiple operations to reduce overhead.
• Thread Safety: Take advantage of the inherent thread safety for concurrent data access.
• Capacity Management: Use the builder pattern to efficiently add or modify multiple items.

Conclusion

The ImmutableDictionary<TKey, TValue> in C# is a valuable collection for applications requiring predictable state and thread safety. By understanding how to use its methods effectively, you can build efficient and reliable collections that are easy to manage.