On 05/17/12 10:47, Roman D. Boiko wrote: > On Thursday, 17 May 2012 at 08:39:21 UTC, Artur Skawina wrote: >> On 05/17/12 10:15, Roman D. Boiko wrote: >>> I mean, is it safe (assuming that we are allowed to mutate blob, and its >>> length is a multiple of C.sizeof)? >>> >>> I do casting from ubyte[] to C[]. >> >> Only if C.ptr ends up properly aligned. There are also aliasing >> issues, which i don't think are sufficiently defined for D (for >> C, it would be legal only because char* is allowed to alias anything). >> >> artur > > Is it possible to ensure? In my case blob is created as > auto blob = cast(ubyte[]) read(fileName); > I assume that alignment is safe. > > But what should I do to be safe in a general case?
Well, you have to assume any /new/ buffers returned are sufficiently aligned; still, slicing the buffers and appending in place can result in arrays that have a legal length (so won't trigger a cast failure at runtime), but are not properly aligned and accessing the elements will fail in different ways (crash, data corruption etc). assert(cast(size_t)data.ptr%data.alignof==0); This assert can be easily triggered eg by doing blob[1..$-4]; blob.assumeSafeAppend(); ++blob.length; auto data = cast(C[]) blob; artur
