Friday, 9 July 2021

Immutable lists in C# - Adding a wrapper class

This article will discuss the immutable collections in C#, more precisely immutable lists of generic type T wrapped inside a class. This makes it possible to easier use immutable lists and these lists can only be altered via functional calls. Remember that an immutable list always returns a new immutable list. For easier use, we can have a wrapper for this. First of, inside Linqpad 5, being used in this article, hit F4. In case you want to use Visual Studio instead, the same code should work there (except Linqpad's Dump method). In the tab Additional referencesNow choose Add Nuget.. Then seach for System.Collections.Immutable. After selecting this Nuget package, choose the tab Additional Namesapce Imports. Now paste this demo code:
 void Main()
	var numbersInImmutableList = new ImmutableWrappedList<int>();
	numbersInImmutableList.AddRange(new[] { 3, 1, 4, 1, 5, 9, 2 }); 
	numbersInImmutableList.AddRange(new[]{ 2, 7, 1, 8, 2, 1, 8 });

public class ImmutableWrappedList<T>  {
	public ImmutableList<T> _internalList;
    	public ImmutableList<T> Contents => _internalList;
	public ImmutableWrappedList()
		_internalList = ImmutableList.Create<T>(); 	
	public void Clear() => _internalList.Clear(); 	
	public void AddRange(IEnumerable<T> itemsToAdd) => _internalList = _internalList.AddRange(itemsToAdd);
	public void Add(T itemToAdd) => _internalList = _internalList.Add(itemToAdd);
	public void Remove(T itemToAdd) => _internalList = _internalList.Remove(itemToAdd);
	public void RemoveAt(int index) => _internalList = _internalList.RemoveAt(index);
	public void Insert(T itemToAdd, int position) => _internalList = _internalList.Insert(position, itemToAdd);

As we can see, the wrapper class can add items to the immutable collections and we also reassign the result modifying operation to the same _internalList field, which has a private setter and is initialized to an empty array in the constructor. This gives you mutability to the immutable collection without having to remember to reassign the variable, which is error prone in itself. Note - we have called the _internalList and you see that we can get thi What is the benefit of this ? Well, although we can reach into the internal collection with the Contents method here, the immutable list is still immutable. If you want to change it, you have to call specific methods here on it offered in the wrapping class. So, data-integrity wise, we have data that only can change via the methods offered in the wrapping class. A collection which is not immutable can be changed in many ways only by giving access to it. We still have control over the data via the wrapper and we make it easier to consume the immutable class by reassigning the collection.

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