Question: My method is as follows

```
  def myMethod(myDouble: Double): Double = myDouble match {
    case Double.NaN => ...
    case _ => ...
  }

```

The IntelliJ debugger is showing NaN but this is not being picked up in my pattern matching. Are there possible cases I am omitting

Answer: 
It is a general rule how 64-bit floating point numbers are compared according to IEEE 754 (not Scala or even Java related, see [NaN](http://en.wikipedia.org/wiki/NaN)):

```
double n1 = Double.NaN;
double n2 = Double.NaN;
System.out.println(n1 == n2);     //false

```

The idea is that `NaN` is a marker value for *unknown* or *indeterminate*. Comparing two unknown values should always yields `false` as they are well... unknown.

---

If you want to use pattern matching with `NaN`, try this:

```
myDouble match {
    case x if x.isNaN => ...
    case _ => ...
}

```

But I think pattern matching will use strict double comparison so be careful with this construct.
You can write an extractor (updated according to bse's comment):

```
object NaN {
  def unapply(d:Double) = d.isNaN
}

0.0/0.0 match {
  case NaN() => println("NaN")
  case x => println("boring " + x)
}
//--> NaN

```