Assigning a static array

[Jonathan M Davis]

On Thursday, April 18, 2013 23:06:32 Brad Anderson wrote:
> Is this supposed to be allowed:
> 
> ubyte[] a;
> ubyte[16] b;
> a = b;
> assert(a.ptr == b.ptr);
> 
> Because if so that makes it terribly easy to do a bug like this
> (as I just saw in IRC):
> 
> struct A
> {
> ubyte[] a;
> this(ubyte c)
> {
> ubyte[16] b;
> b[] = c;
> this.a = b; // a now points at an immediately invalid
> static array
> }
> }

Yes, that's legal, though it should arguably be @system, since it's doing 
essentially the same thing as

int i;
int* p = &i;

which _is_ @system. The compiler doesn't currently consider slicing a static 
array in general to be @system though, much as it should ( 
http://d.puremagic.com/issues/show_bug.cgi?id=8838 ). I could see an argument 
that it should have to be

a = b[];

so that the slicing is explicit instead of just

a = b;

where it's implicit, but AFAIK, that's not currently required. You have to be 
very careful when slicing static arrays. If it were up to me, exlicit slicing 
would _always_ be required when slicing a static array, even when calling 
functions which take a dynamic array, but that's not how it works 
unfortunately.

- Jonathan M Davis