Refined types [almost OT]

[Meta via Digitalmars-d]

On Sunday, 12 October 2014 at 16:21:50 UTC, bearophile wrote:
What happens if one of these conditions fails? Is an exception 
thrown? Note that you can also sort of do this using template 
constraints, but that of course only works at compile time:

double get2dimensional(int n, int m, int i, int j, double[] arr)()
if (n >= 0
     && m >= 0
     && 0 <= i
     && i < m
     && 0 <= j
     && j < n
     && arr.length == m * n)
{
     return arr[i * n + j];
}