Choosing the right collection type

• Great docs here

Important Note

ICollection IList IEnumerable ISet

Concrete Types: Collection List HashSet SortedSet

SO: Why HashSet over a List https://stackoverflow.com/a/10735440/190476

NOTE: C# HashSet mathematical equality needs to be checked using SetEquals

SO: Mathematical quality by default

public sealed class MathSet<T> : HashSet<T>, IEquatable<MathSet<T>>
{
    public override int GetHashCode() => this.Select(elt => elt.GetHashCode()).Sum().GetHashCode();

    public bool Equals(MathSet<T> obj) => SetEquals(obj);

    public override bool Equals(object obj) => Equals(obj as MathSet<T>);

    public static bool operator ==(MathSet<T> a, MathSet<T> b) =>
        ReferenceEquals(a, null) ? ReferenceEquals(b, null) : a.Equals(b);

    public static bool operator !=(MathSet<T> a, MathSet<T> b) => !(a == b);
}

References

• Code Project Fun with custom collections
• Choosing collection type MS Docs
• Set based .NET collections Code Project
  • Related concept: Hash code and GetHashCode Stackoverflow To be stored in a hash based collection such as Hashset or Dictionary, an object needs to implement a GetHashCode method. This method is defined on the Object base class but must be customised such that the same starting value produces the same hash.