CSHARP.IDEF.NOEQUALS : Missing Equals Override (C#)

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CSHARP.IDEF.NOEQUALS : Missing Equals Override (C#)

Summary

Redefinitions of the Equals()/GetHashCode() methods from System.Object must be consistent in the sense that, for instance, if two objects are Equals() then GetHashCode() must yield the same value on both. The validity of such a property is in general undecidable, but most incorrect definitions amount to simple cases, where one of the two methods is missing. However, it is often correct to redefine only one of those methods and the analyzer is aware of many such situations.

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

Properties

Example

using System;
using System.Diagnostics;

namespace DocumentationExamples
{

    public class BadEq
    {
        public static bool verbose;
        private readonly static string[] arr = new string[] { "verbose" };
        public static void Main(string[] args)
        {
            if (args.Length > 0)
                Debug.Assert(!args[0].Equals(""));   // Comparison to Empty String (C#) warning issued here
            if (args.Length > 0 && args[0] == "verbose")
                verbose = true;
            if (args.Equals(arr))                    // equals on Array (C#) warning issued here
                verbose = true;
            if (args.Length > 0)
            {
                BadEq m = new BadEq();
                Console.WriteLine(m.Test(args[0]));
                Console.WriteLine(m.WeAreRedefined());
            }
        }
        private bool Test(object o)
        {
            return o == this;                        // == Always Fails (C#)  warning issued here
                                                     // - operands have incompatible types
        }
        public bool WeAreRedefined()
        {
            return !GetType().Equals(typeof(BadEq)); // Missing Equals Override (C#) warning issued here
        }
        
        public bool EqualityTest()
        {
            object name = "myname";
            char[] values = { 'm', 'y', 'n', 'a', 'm', 'e' };
            object myName = new string(values);
            return name == myName;                   // Should Use equals() Instead of == (C#) warning issued here
        }
    }
}

public static bool verbose;
private readonly static string[] arr = new string[] { "verbose" };
public static void Main(string[] args)
{
    if (args.Length > 0)
        Debug.Assert(!string.IsNullOrEmpty(args[0]));
    if (args.Length > 0 && args[0].Equals("verbose"))
        verbose = true;
    if (args.SequenceEqual(arr))
        verbose = true;
    if (args.Length > 0)
    {
        BadEq m = new BadEq();
        //Console.WriteLine(m.Test(args[0]));
        Console.WriteLine(m.WeAreRedefined());
    }
}

public bool WeAreRedefined()
{
    return GetType() != typeof(BadEq);
}

Resolution

Make Equals() consistent with GetHashCode(). In many cases, this just amounts to provide the missing definition for one of them.

Relevant Configuration File Parameters

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