CSHARP.CLASS.IOF.T : Instanceof Always True (C#)

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CSHARP.CLASS.IOF.T : Instanceof Always True (C#)

Summary

This checker looks for is operators that are useless, in the sense that they are always true or always false and can hence be removed from the code. This can improve the efficiency of the program. Moreover, a useless is test is often the sign of a programming bug.

Properties

Example

using System;

namespace DocumentationExamples
{
    public class UselessInstanceof
    {
        public static void Main(string[] args)
        {
            UselessInstanceofA a = new UselessInstanceofB();
            switch (DateTime.Now.Millisecond % 3)
            {
                case 0:
                case 1:
                    a = new UselessInstanceofA(); break;
                case 2:
                    a = new UselessInstanceofC(); break;
            }
            if (a is UselessInstanceofC)
                Foo(a);
        }
        private static void Foo(UselessInstanceofA par)
        {
            if (par is UselessInstanceofB)  // "Instanceof Always True (C#)" warning issued here
                Console.WriteLine("par is a B");
        }
    }
    public class UselessInstanceofA { }
    public class UselessInstanceofB : UselessInstanceofA { }
    public class UselessInstanceofC : UselessInstanceofB { }
}

Resolution

Check if the is operator can be actually removed and that it is not the sign of an actual programming bug.

Relevant Configuration File Parameters

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