using System;

using System.Collections.Generic;

​

static class Program

{

    static void Main()

    {

        var redBox = new Box(8, 8, 4);

        var blueBox = new Box(6, 8, 4);

        var greenBox = new Box(4, 8, 8);

​

        var boxes = new[] { redBox, blueBox, greenBox };

​

        var boxToFind = new Box(4, 8, 8);

​

        var foundByDimension = boxes.FindFirst(boxToFind);

​

        Console.WriteLine($"Found box {foundByDimension} by dimension.");

​

        var foundByVolume = boxes.FindFirst(boxToFind, new BoxEqVolume());

​

        Console.WriteLine($"Found box {foundByVolume} by volume.");

    }

}

​

public static class CollectionExtensions

{

    public static T FindFirst<T>(

        this IEnumerable<T> collection, T itemToFind, IEqualityComparer<T> comparer = null)

    {

        comparer = comparer ?? EqualityComparer<T>.Default;

​

        foreach (var item in collection)

        {

            if (comparer.Equals(item, itemToFind))

            {

                return item;

            }

        }

​

        throw new InvalidOperationException("No matching item found.");

    }

}

​

public class BoxEqVolume : EqualityComparer<Box>

{

    public override bool Equals(Box b1, Box b2)

    {

        if (object.ReferenceEquals(b1, b2))

            return true;

​

        if (b1 is null || b2 is null)

            return false;

​

        return b1.Volume == b2.Volume;

    }

​

    public override int GetHashCode(Box box) => box.Volume.GetHashCode();

}

​

public class Box : IEquatable<Box>

{

    public Box(int height, int length, int width)

    {

        this.Height = height;

        this.Length = length;

        this.Width = width;

    }

​

    public int Height { get; }

    public int Length { get; }

    public int Width { get; }

​

    public int Volume => Height * Length * Width;

​

    public bool Equals(Box other)

    {

        if (other is null)

            return false;

​

        return this.Height == other.Height && this.Length == other.Length

            && this.Width == other.Width;

    }

​

    public override bool Equals(object obj) => Equals(obj as Box);

    public override int GetHashCode() => (Height, Length, Width).GetHashCode();

    //public override int GetHashCode() => this.GetHashCode();

​

    public override string ToString() => $"{Height} x {Length} x {Width}";

}

​

/* This example produces the following output:

 *

    Found box 4 x 8 x 8 by dimension.

    Found box 8 x 8 x 4 by volume.

 */