Question

If I can implicitly cast an integer value to a double, like:

int a = 4;    
double b = a;
// now b holds 4.0

Why can I not do this:

int[] intNumbers = {10, 6, 1, 9};    
double[] doubleNumbers2 = intNumbers.Cast<double>().ToArray();

I get a “Specified cast is not valid” InvalidCastException exception.

Doing the opposite (casting from double to int) results in the same error.

What am I doing wrong?

Answer 1

Well, you have incorrect expectations of Cast, that’s all – it’s meant to deal with boxing/unboxing, reference and identity conversions, and that’s all. It’s unfortunate that the documentation isn’t as clear as it might be 🙁

The solution is to use Select:

doubleNumbers2 = intNumbers.Select(x => (double) x).ToArray();