# V659. Functions' declarations with 'Foo' name differ in 'const' keyword only, while these functions' bodies have different composition. It is suspicious and can possibly be an error.

The analyzer has detected two functions with identical names in the code. The functions are different in the constancy parameter.

Function declarations may differ in:

- the constancy of the returned value;
- the constancy of arguments;
- the constancy of the function itself (in case of class methods).

Although the names of the functions coincide, they work differently. It may be a sign of an error.

Consider a simple case:

    class CLASS {
      DATA *m_data;
    public:
      char operator[](size_t index) const {
        if (!m_data || index >= m_data->len)
          throw MyException;
        return m_data->data[index];
       }

      char &operator[](size_t index) {
        return m_data->data[index];
      }
    };

The constant function 'operator[]' contains a check so that an exception is thrown in case of an error. A non-constant function doesn't contain such a check. This is most likely a slip-up that should be fixed.

The analyzer takes into account a set of different situations when the differences in function bodies are reasonable. But we cannot account for all the exceptional cases. So, if the analyzer has generated a false positive, you can suppress it using the "//-V659" comment.