ValueCollection.cs

using System.Collections.ObjectModel;

#nullable enable

namespace Nemesis.Essentials.Design;

public class ValueCollection<T>(IList<T> list, IEqualityComparer<T>? equalityComparer = null)
    : Collection<T>(list), IEquatable<ValueCollection<T>>, IFormattable
{
    private readonly IEqualityComparer<T> _equalityComparer = equalityComparer ?? EqualityComparer<T>.Default;

    public ValueCollection() : this(new List<T>()) { }

    public ValueCollection(IEqualityComparer<T>? equalityComparer = null) : this(new List<T>(), equalityComparer) { }

    public bool Equals(ValueCollection<T>? other)
    {
        if (other is null) return false;

        if (ReferenceEquals(this, other)) return true;

        using var enumerator1 = GetEnumerator();
        using var enumerator2 = other.GetEnumerator();

        while (enumerator1.MoveNext())
            if (!enumerator2.MoveNext() || !(_equalityComparer!).Equals(enumerator1.Current, enumerator2.Current))
                return false;

        return !enumerator2.MoveNext(); //both enumerations reached the end
    }

    public override bool Equals(object? obj) => obj is { } && (ReferenceEquals(this, obj) || obj is ValueCollection<T> coll && Equals(coll));

    public override int GetHashCode() =>
        unchecked(Items.Aggregate(0,
            (current, element) => (current * 397) ^ (element is null ? 0 : _equalityComparer.GetHashCode(element))
        ));

    public string ToString(string? format, IFormatProvider? formatProvider)
        => "[" + string.Join(", ", this.Select(e => FormatValue(e, formatProvider))) + "]";

    public override string ToString() => ToString(null, CultureInfo.CurrentCulture);

    private static string? FormatValue(object? value, IFormatProvider? formatProvider) =>
        value switch
        {
            null => "∅",
            bool b => b ? "true" : "false",
            string s => $"\"{s}\"",
            char c => $"\'{c}\'",
            DateTime dt => dt.ToString("o", formatProvider),
            IFormattable @if => @if.ToString(null, formatProvider),
            IEnumerable ie => "[" + string.Join(", ", ie.Cast<object>().Select(e => FormatValue(e, formatProvider))) + "]",
            _ => value.ToString()
        };
}