Pointer arrays

In an unsafe context, arrays of pointers can be constructed. Only some of the conversions that apply to other array types are allowed on pointer arrays:

· The implicit reference conversion (§6.1.6) from any array-type to System.Array and the interfaces it implements also applies to pointer arrays. However, any attempt to access the array elements through System.Array or the interfaces it implements will result in an exception at run-time, as pointer types are not convertible to object.

· The implicit and explicit reference conversions (§6.1.6, §6.2.4) from a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its generic base interfaces never apply to pointer arrays, since pointer types cannot be used as type arguments, and there are no conversions from pointer types to non-pointer types.

· The explicit reference conversion (§6.2.4) from System.Array and the interfaces it implements to any array-type applies to pointer arrays.

· The explicit reference conversions (§6.2.4) from System.Collections.Generic.IList<S> and its base interfaces to a single-dimensional array type T[] never applies to pointer arrays, since pointer types cannot be used as type arguments, and there are no conversions from pointer types to non-pointer types.

These restrictions mean that the expansion for the foreach statement over arrays described in §8.8.4 cannot be applied to pointer arrays. Instead, a foreach statement of the form

foreach (V v in x) embedded-statement

where the type of x is an array type of the form T[,,…,], n is the number of dimensions minus 1 and T or V is a pointer type, is expanded using nested for-loops as follows:

{
T[,,…,] a = x;
V v;
for (int i0 = a.GetLowerBound(0); i0 <= a.GetUpperBound(0); i0++)
for (int i1 = a.GetLowerBound(1); i1 <= a.GetUpperBound(1); i1++)
…
for (int in = a.GetLowerBound(n); in <= a.GetUpperBound(n); in++) {
v = (V)a.GetValue(i0,i1,…,in);
embedded-statement
}
}

The variables a, i0, i1, … in are not visible to or accessible to x or the embedded-statement or any other source code of the program. The variable v is read-only in the embedded statement. If there is not an explicit conversion (§18.4) from T (the element type) to V, an error is produced and no further steps are taken. If x has the value null, a System.NullReferenceException is thrown at run-time.