How Does Resharper Know “Expression is always true”?

Question

Check out the following code:

private void Foo(object bar)
{
   Type type = bar.GetType();

    if (type != null) // Expression is always true
    {   
    }         


        

Answer 1

Yes, it basically has knowledge of some well-known methods. You should find the same for string concatenation too, for example:

string x = null;
string y = null;
string z = x + y;

if (z == null)
{
    // ReSharper should warn about this never executing
}

Now the same information is also becoming available via Code Contracts - I don't know whether JetBrains is hooking directly into this information, has its own database, or a mixture of the two.