When you implement IComparable or IComparable<T> on a class you should also override Equals(object)
and overload the comparison operators (==, !=, <, <=, >,
>=). That’s because the CLR cannot automatically call your CompareTo implementation from Equals(object) or
from the base comparison operator implementations. Additionally, it is best practice to override GetHashCode along with
Equals.
This rule raises an issue when a class implements IComparable without also overriding Equals(object) and the comparison
operators.
Noncompliant code example
public class Foo: IComparable // Noncompliant
{
public int CompareTo(object obj) { /* ... */ }
}
Compliant solution
public class Foo: IComparable
{
public int CompareTo(object obj) { /* ... */ }
public override bool Equals(object obj)
{
var other = obj as Foo;
if (object.ReferenceEquals(other, null))
{
return false;
}
return this.CompareTo(other) == 0;
}
public int GetHashCode() { /* ... */ }
public static bool operator == (Foo left, Foo right)
{
if (object.ReferenceEquals(left, null))
{
return object.ReferenceEquals(right, null);
}
return left.Equals(right);
}
public static bool operator > (Foo left, Foo right)
{
return Compare(left, right) > 0;
}
public static bool operator < (Foo left, Foo right)
{
return Compare(left, right) < 0;
}
public static bool operator != (Foo left, Foo right)
{
return !(left == right);
}
}
