Can a [pure] function throw an exception?

Question

Is it OK for a function that can throw an exception to have the [pure] attribute?

Answer 1

According to

https://msdn.microsoft.com/en-us/library/system.diagnostics.contracts.pureattribute(v=vs.110).aspx

PureAttribute attribute

Indicates that a type or method is pure, that is, it does not make any visible state changes.

So it's quite possible to throw an exception from such a method e.g.

// factorial is a pure function: no state will be changed, 
// just a computation 
[Pure]
public static BigInteger Factorial(BigInteger value) {
  // We can't return infinity with BigInteger and that's why have to throw the exception 
  if (value < 0)
    throw new ArgumentOutOfRangeException("value", "value must be non-negative"); 

  ...
}

And what if I call this pure method as

  BigInteger result = Factorial(1000000000);

one of the possible outcomes is OutOfMemory exception thrown