IEquatable.dib

#!markdown

# IEquatable

#!markdown

### Plain Class

#!csharp

public class ComplexNumber
{
  public int Imaginary { get; set; }
  public int Real { get; set; }

  public ComplexNumber(int real, int imaginary)
  {
    Imaginary = imaginary;
    Real = real;
  }

  public override string ToString()
  {
    return $"{Real} + {Imaginary}i";
  }
}

#!csharp

display("");
var c1 = new ComplexNumber(1, 2);
var c2 = new ComplexNumber(1, 2);

Console.WriteLine($"c1 == c2: {c1.Equals(c2)}");

List<ComplexNumber> list = new List<ComplexNumber>();
list.Add(c1);

Console.WriteLine($"c1 in List: {list.Contains(c1)}");
Console.WriteLine($"c2 in List: {list.Contains(c2)}");
Console.WriteLine($"c2 in List: {list.IndexOf(c2)}");

#!markdown

### IEquatable implementation

#!csharp

public class ComplexNumberWithInterface: ComplexNumber, IEquatable<ComplexNumberWithInterface>
{
    public ComplexNumberWithInterface(int real, int imaginary): base(real, imaginary) {}

    public bool Equals(ComplexNumberWithInterface other)
    {
        return other.Real == this.Real && other.Imaginary == this.Imaginary;
    }
}

#!csharp

display("");
var c1 = new ComplexNumberWithInterface(1, 2);
var c2 = new ComplexNumberWithInterface(1, 2);

Console.WriteLine($"c1 == c2: {c1.Equals(c2)}");

List<ComplexNumberWithInterface> list = new List<ComplexNumberWithInterface>();
list.Add(c1);

Console.WriteLine($"c1 in List: {list.Contains(c1)}");
Console.WriteLine($"c2 in List: {list.Contains(c2)}");
Console.WriteLine($"c2 in List: {list.IndexOf(c2)}");
Console.WriteLine($"c2 in List: {list.Contains(new ComplexNumberWithInterface(1, 2))}");

#!markdown

### Full Implementation

#!csharp

Console.WriteLine($"c1 == c2: {c1.Equals((object)c2)}");
Console.WriteLine($"c1 == c2: {c1 == c2}");

#!csharp

public class ComplexNumberFull: ComplexNumber, IEquatable<ComplexNumberFull>
{
    public ComplexNumberFull(int real, int imaginary): base(real, imaginary) {}

    public bool Equals(ComplexNumberFull other)
    {
        Console.WriteLine("Equals(ComplexNumberFull other)");
        return other.Real == this.Real && other.Imaginary == this.Imaginary;
    }

    public override bool Equals(object? other)
    {
        Console.WriteLine("Equals(object? other)");
        return other switch
        {
            ComplexNumberFull cn => this.Equals(cn),
            _ => false
        };
    }

    public override int GetHashCode()
    {
        return Real.GetHashCode() * 10 + Imaginary.GetHashCode();
    }

    public static bool operator ==(ComplexNumberFull cn1, ComplexNumberFull cn2)
    {
        Console.WriteLine("operator ==");
        return cn1.Equals(cn2);
    }

    public static bool operator !=(ComplexNumberFull cn1, ComplexNumberFull cn2)
    {
        Console.WriteLine("operator !=");
        return !cn1.Equals(cn2);
    }
}

#!csharp

display("");
var c1 = new ComplexNumberFull(1, 2);
var c2 = new ComplexNumberFull(1, 2);

Console.WriteLine($"c1 == c2: {c1.Equals(c2)}");

List<ComplexNumberFull> list = new List<ComplexNumberFull>();

list.Add(new ComplexNumberFull(3, 4));
list.Add(c1);

Console.WriteLine($"c1 in List: {list.Contains(c1)}");
Console.WriteLine($"c2 in List: {list.Contains(c2)}");
Console.WriteLine($"c2 in List: {list.IndexOf(c2)}");

Console.WriteLine($"c1 == c2: {c1.Equals((object)c2)}");
Console.WriteLine($"c1 == c2: {c1 == c2}");