Modern C# and .NET Tutorial: Cross-Platform Basics/

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Understanding Collection Choices

Understanding Collection Choices

Learn about common collection types, their implementations, and when to use each type.

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Improving performance by ensuring the capacity of a collection

Since .NET 1.1, types like StringBuilder have had a method named EnsureCapacity that can pre-size its internal storage array to the expected final size of the string. This improves performance because it does not have to repeatedly increment the array size as more characters are appended. Since .NET Core 2.1, types like Dictionary and HashSet have also had EnsureCapacity. In .NET 6 and later, collections like List, Queue, and Stack now have an EnsureCapacity method too, as shown in the following code:

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List<string> names = new();
names.EnsureCapacity(10_000);
// load ten thousand names into the list

There are several different choices of collections that we can use for different purposes: lists, dictionaries, stacks, queues, sets, and many other, more specialized collections.

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Generic collection
Generic collection

Lists

Lists, that is, a type that implements IList, are ordered collections, as shown in the following code:

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namespace System.Collections.Generic;
[DefaultMember("Item")] // also known as this indexer
public interface IList<T> : ICollection<T>, IEnumerable<T>, IEnumerable
{
  T this[int index] { get; set; }
  int IndexOf(T item);
  void Insert(int index, T item);
  void RemoveAt(int index);
}

IList derives from ICollection so it has the ...