using System;

using System.Collections.Generic;

using System.Text;

​

using NUnit.Framework;

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#nullable enable

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//https://stackoverflow.com/questions/78419412/uniquness-of-a-record-containing-a-collection

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/*

https://learn.microsoft.com/en-us/dotnet/fundamentals/runtime-libraries/system-object-equals#guidelines-for-reference-types

​

 - You should not override Equals on a mutable reference type. 

​

*/

​

using System.Collections.Immutable;

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public record Person(string FirstName, ImmutableHashSet<int> FavouriteNumbers)

{

    public Person(string FirstName, IEnumerable<int> FavouriteNumbers) : this(FirstName, ImmutableHashSet.CreateRange(FavouriteNumbers)) { }

    // Use of HashCode.Combine() suggested by Dmitry Bychenko in https://stackoverflow.com/a/78419565

    public override int GetHashCode() => HashCode.Combine(FirstName, FavouriteNumbers?.Count);

    //https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/record#value-equality

    public virtual bool Equals(Person? other) => 

        object.ReferenceEquals(other, this)

        || (!object.ReferenceEquals(other, null) && this.GetType() == other.GetType() && this.FirstName == other.FirstName && this.FavouriteNumbers.SetEquals(other.FavouriteNumbers));

​

    protected virtual bool PrintMembers(StringBuilder sb)

    {

        //https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/record#printmembers-formatting-in-derived-records

        //Make FavouriteNumbers be printed as a comma-separated list of values.

        sb.Append(nameof(FirstName)).Append(" = ").Append(FirstName)

            .Append(", ")

            .Append(nameof(FavouriteNumbers)).Append(" = ").AppendJoin(',', FavouriteNumbers);

        return true;

    }

}

public class Program

{

    public static void Main()

    {

        var person = new Person("Foo", new [] { 1, 2, 3 });

        var p2 = new Person("Foo", ImmutableHashSet.Create(new [] { 3, 2, 1 }));

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        var eq = person == p2;

        Console.WriteLine($"{person} == {p2} = {eq}");

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        Assert.That(eq);

        var p3= new Person("Foo", new [] { 1, 2, 4 });

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        var eq3 = person == p3;

        Console.WriteLine($"{person} == {p3} = {eq3}");

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        Assert.That(!eq3);

        var modifiedPerson = person with { 

            FavouriteNumbers = person.FavouriteNumbers.Remove(3).Add(5) 

        };

        Console.WriteLine($"\nmodifiedPerson = {modifiedPerson}");

        Assert.That( person != modifiedPerson);

        var newName = person with { FirstName = "Bar" };

        Assert.That( person != newName);

    }

}

​