struct / cast / ? design problem

[ketmar via Digitalmars-d-learn]

On Mon, 16 Mar 2015 11:18:16 -0700, Charles Hixson via Digitalmars-d-learn
wrote:

> My current best answer is to turn the "unused" into a vector of bytes,
> and then pass that to the using routines as a ref.  This still is wide
> open to errors at the calling end, but the BlockHead end can ensure that
> the length of the vector remains constant whenever it accesses it (well,
> whenever the head is being written to disk.  The byte vector would be a
> static array at the BlockHead end.  This would seem to allow the using
> end to cast the byte vector into an appropriate struct for its own use,
> and that writes to it would be seen by BlockHead as writes to the
> header...but only to restricted parts of the header.  The problem here
> is that the ref array might allow itself to be resized at the user end.
> That's not a problem as long as the resizing is to something smaller,
> but I'm not sure what happens if it gets resized to something larger. It
> looks like allowing a buffer overflow.

if you passing the array, not a slice, it can't be resized. i.e.:

  void foo (ref ubyte[8] a) {
    a[2] = 42;
    //a.length = 6; // this will not compile: constant a.length is not an 
lvalue
  }

  void main () {
    ubyte[8] aa;
    assert(aa[2] == 0);
    foo(aa);
    assert(aa[2] == 42);
  }
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: not available
URL: <http://lists.puremagic.com/pipermail/digitalmars-d-learn/attachments/20150316/72a97c0a/attachment.sig>