How should I implement equality checking for classes that have objects of other classes as member?

Question

I have a Student class that has an object of class Name.

At this point, the equality check of the Student class returns false, and I don't know why.

public class Student : IEquatable<Student>
{
  public Name Name { get; }

  public Student(Name name) => Name = name;

  public bool Equals(Student other)
  {
    if (ReferenceEquals(this, other))
      return true;
    if (ReferenceEquals(other, null))
      return false;

    return Name == (other.Name);
  }
}

public class Name : IEquatable<Name>
{
  public string First { get; }

  public Name(string first) => First = first;

  public bool Equals(Name other)
  {
    if (ReferenceEquals(this, other))
      return true;
    if (ReferenceEquals(other, null))
      return false;

    return First == other.First;
  }
}

var s1 = new Student(new Name("A"));
var s2 = new Student(new Name("A"));

Console.WriteLine(s1.Equals(s2).ToString());

Of course, doing the equality check this way will return true.

var s1 = new Student(new Name("A"));
var s2 = s1;

Console.WriteLine(s1.Equals(s2).ToString());

Can you tell me what I'm doing wrong?

Answer 1

Solution 1 (Recommended)

Since you had implemented IEquatable interface for Name class, just calls .Equals() in Student class.

public class Student : IEquatable<Student>
{
    public Name Name { get; }

    public Student(Name name) => Name = name;
    public bool Equals(Student other)
    {
        if (ReferenceEquals(this, other))
            return true;
        if (ReferenceEquals(other, null))
            return false;
        return Name.Equals(other.Name); // Replaces with .Equals
    }
}

Sample .NET Fiddle (Solution 1)

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Solution 2

Or you need to implement operator overloading for the == and != operators.

If you use == operator in:

public class Student : IEquatable<Student>
{
    ...

    public bool Equals(Student other)
    {
        ...

        return Name == (other.Name);
    }
}

public class Name : IEquatable<Name>
{
    ...
    
    public static bool operator == (Name a, Name b)
    {
        return a.First == b.First;
    }
    
    public static bool operator != (Name a, Name b)
    {
        return a.First != b.First;
    }
}

Sample .NET Fiddle (Solution 2)