CodeQL documentation

Equals on incomparable types

ID: cs/equals-on-unrelated-types
Kind: problem
Severity: error
Precision: high
Tags:
   - reliability
   - correctness
Query suites:
   - csharp-security-and-quality.qls

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Calling x.Equals(y) on incomparable types will almost always return false. If two classes do not have a common parent class their instances are considered incomparable.

Recommendation

Carefully check the code for errors.

Example

In this example both calls to the Equals method will always return false regardless of the contents of the ArrayList or String because ArrayLists and Strings are incomparable.

using System.Collections;

class IncomparableEquals
{
    public static void Main(string[] args)
    {
        ArrayList apple = new ArrayList();
        String orange = "foo";
        Console.WriteLine(apple.Equals(orange)); // BAD
        Console.WriteLine(orange.Equals(apple)); // BAD
    }
}

References