On 02/06/2017 03:00 PM, Bastiaan Veelo wrote:
> In "Numerical Recipes in C", section 1.2, Press et al. propose an easy
> solution using an offset pointer:
>
> float b[4], *bb;
> bb = b - 1;
>
> Thus bb[1] through bb[4] all exist, no space is wasted nor is there a
> run-time overhead.
>
> I have tried to adapt the internals of my struct to Press' approach, but
> it seems to me it is not that easy in D -- or I'm just not proficient
> enough. Can someone here show me how that could be done?
struct StaticArray(T, ptrdiff_t first, ptrdiff_t last) {
T[last - first + 1] _payload;
If the static array has to be a member like that (as opposed to a
dynamic one), you need an extra member:
T* _ptr;
Because structs cannot have default constructors, you need an init()
function to establish the invariant:
void init() {
this._ptr = _payload.ptr - first;
}
Of course, that relies on the fact that _payload.ptr - first is a valid
address to hold in a pointer.
[OT]:
// Commented-out as it seems dangerous because _payload does not
// have the same semantics as StaticArray.
//
// alias _payload this;
Which means, you would implement length() yourself:
size_t length() {
return _payload.length;
}
Then you use _ptr when indexing:
// Support e = arr[5];
ref T opIndex(ptrdiff_t index) {
assert(index >= first);
assert(index <= last);
return *(_ptr + index);
}
Ali
