constness for arrays

[David Medlock]

xs0 wrote:
> As has been discussed, the lack of something like C++ const hurts most 
> when using arrays, as you can't code around it like with classes, 
> structs or primitives (with the latter two you can just pass by value, 
> for classes you can make readonly versions). The fact that inbuilt 
> strings are also arrays makes the problem occur often.
> 
> I was wondering whether the following would resolve that issue:
> 
> - the top bit of arrays' .length becomes an indicator of the 
> readonlyness of the array reference
> 
<snip>

I like it except it drops the max array size by half, doesn't it?

Since we are talking about dynamic arrays here, why not just:

1. add a flags byte or short to the internal array structure to hold it.

2. make the pointers lower bit hold it- this of course assumes the 
pointer is at least word-aligned.  I am not sure if this would conflict 
with structs which are align(1).

-DavidM