# V3001. There are identical sub-expressions to the left and to the right of the 'foo' operator.

The analyzer has detected a code fragment that is very likely to have a logical error in it. The program text contains an operator (<, >, <=, >=, ==, !=, &&, ||, -, /, &, |, ^) whose both operands are identical subexpressions.

Consider this example:

    if (a.x != 0 && a.x != 0)

In this case, the '&&' operator is surrounded by identical subexpressions "a.x != 0", which enables the analyzer to detect a mistake made through carelessness. A correct version of this code, which won't trigger the diagnostic, should look as follows:

    if (a.x != 0 && a.y != 0)

Here's another example of a mistake detected by the analyzer in an application's code:

    class Foo {
      List<int> Childs { get; set; }
      ...
      public bool hasChilds() { return(Childs[0] > 0 || Childs[0] > 0); }
      ...
    }

In this case, although the code compiles well and without any warnings, it just doesn't make sense. Its correct version should look like this:

    public bool hasChilds(){ return(Childs[0] > 0 || Childs[1] > 0);}

The analyzer compares the code blocks, taking into account inversion of the expression's parts in relation to the operator. For example, it will detect the error in the following code:

    if (Name.Length > maxLength && maxLength < Name.Length)

This diagnostic is classified as:

CWE-570 CWE-571

You can look at examples of errors detected by the V3001 diagnostic.