CodeQL documentation

Useless type test

ID: cs/useless-type-test
Kind: problem
Security severity: 
Severity: warning
Precision: medium
   - maintainability
   - language-features
   - external/cwe/cwe-561
Query suites:
   - csharp-security-and-quality.qls

Click to see the query in the CodeQL repository

For any type B, an instance of a type derived from B is also an instance of B. There is no need to test for this explicitly.


Remove the useless type test.


In this example class Sub extends class Super. A new instance of Sub, sub is initialized and checked to see if it is an instance of Super . Since Sub extends Super then there is no need to test that sub is a Super because it is guaranteed to be the case.

class UselessTypeTest
    class Super { }
    class Sub : Super { }

    static void Main(string[] args)
        Sub sub = new Sub();
        if (sub is Super)
            Console.WriteLine("Surprise! sub is a Super!");
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