CSHARP.COMPARE.CTO.NONCOMP : compareTo in Non-Comparable Class (C#)

Summary

CompareTo() is defined in a class that is not an instance of System.IComparable.

A class C that implements the raw interface System.IComparable must implement the CompareTo(Object) method. If C is made to implement the non-raw interface System.IComparable<C>, then it must implement the CompareTo(C) method instead.

Moreover, it is good practice to make CompareTo() consistent with Equals(): if the comparison of two objects yields 0, then they should be equal. The validity of this implication is in general undecidable. There are, however, frequent situations when, typically, this implication does not hold. An example is when Equals() is inherited from System.Object.

This checker verifies that CompareTo(Object) is defined for classes implementing the raw System.IComparable interface, instead of the (possibly more logical) method CompareTo(C). Moreover, it verifies the consistency of CompareTo() wrt Equals().

Inconsistent definitions of CompareTo()/Equals() induce unexpected behaviors when objects are put inside most sorted collection classes of the standard .NET library.

Properties

WARNING_FILTER += discard class="compareTo in Non-Comparable Class (C#)"

Example

  public class MyClass
    {

        public int CompareTo(object obj) // "compareTo in Non-Comparable Class (C#)" warning issued here
        {
            //...

            return 0;

            //...
        }
        
         //...
    }

In this example, the programmer should rewrite the code as follows.

  public class MyClass : System.IComparable
    {

        public int CompareTo(object obj)
        {
            //...

            return 0;

            //...
        }
        
         //...
    }
}

Resolution

Use the non-raw interface System.IComparable<C>; make Equals() consistent with CompareTo(). In most cases, this just amounts to providing the missing definition of Equals().

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

• REPORT_SIMILAR_WARNINGS
• WARNING_FILTER