What is the difference between IComparable and IEquatable?

Question

both interfaces seem to compare objects for equality, and what are the main differences between them?

Answer 1

IEquatable checks if two objects are equal.

IComparable imposes a general order on the compared objects.

For example, IEquatable tells you that 5 is not 7. IComparable tells you that 5 is up to 7.

Answer 2

IEquatable<T> for equality.

IComparable<T> for order.

Answer 3

In addition to Greg D's answer:

You can implement IComparable without implementing IEquatable for a class where partial ordering makes sense and where you definitely want the consumer to conclude that just because CompareTo () returns zero does not mean that the objects are equal (for anything except sorting).

Answer 4

As indicated on the MSDN page for IEquatable :

The IComparable interface defines the CompareTo method, which determines the sort order of instances implementing the type. The IEquatable interface defines an Equals method that determines the equality of implementation type instances.

Equals vs CompareTo

Answer 5

IComparable <T> defines a type-specific comparison method that can be used to organize or sort objects.

IEquatable <T> defines a generic method that can be used to determine equality.

---

Let's say you have a Person class

 public class Person { public string Name { get; set; } public int Age { get; set; } } Person p1 = new Person() { Name = "Person 1", Age = 34 }; Person p2 = new Person() { Name = "Person 2", Age = 31 }; Person p3 = new Person() { Name = "Person 3", Age = 33 }; Person p4 = new Person() { Name = "Person 4", Age = 26 }; List<Person> people = new List<Person> { p1, p2, p3, p4 }; 

You can use people.Sort(); to sort these objects people.Sort(); ,

But it will be an exception.

Framework does not know how to sort these objects. You must tell how to sort the implementation of the IComparable interface.

 public class Person : IComparable { public string Name { get; set; } public int Age { get; set; } public int CompareTo(object obj) { Person otherPerson = obj as Person; if (otherPerson == null) { throw new ArgumentNullException(); } else { return Age.CompareTo(otherPerson.Age); } } } 

This will allow you to sort the array correctly using the Sort() method.

---

Further for comparison of two objects you can use the Equals() method.

 var newPerson = new Person() { Name = "Person 1", Age = 34 }; var newPersonIsPerson1 = newPerson.Equals(p1); 

This will return false because the Equals method does not know how to compare two objects. Therefore, you need to implement the IEquatable interface and tell the platform how to conduct the comparison. Continuing the previous example, it will look like this.

 public class Person : IComparable, IEquatable<Person> { //Some code hidden public bool Equals(Person other) { if (Age == other.Age && Name == other.Name) { return true; } else { return false; } } }