What are the preconditions of newArray#

Simon Marlow marlowsd at gmail.com
Tue Aug 23 21:47:17 CEST 2011

An Array# of size zero is a perfectly reasonable thing.  If it doesn't 
work, it should (and I vaguely recall making it work at some point in 
the past, but perhaps I failed to add a test and as a result it has 


On 22/08/11 17:08, Johan Tibell wrote:
> I agree (unless it has a performance cost). I had to fix a couple of
> bugs in my code associated with generating zero-length arrays.
> On Mon, Aug 22, 2011 at 5:54 PM, Edward Kmett<ekmett at gmail.com>  wrote:
>> It would still be nice to have a consistent base case.
>> On Mon, Aug 22, 2011 at 3:43 AM, Johan Tibell<johan.tibell at gmail.com>
>> wrote:
>>> On Mon, Aug 22, 2011 at 5:55 AM, Edward Z. Yang<ezyang at mit.edu>  wrote:
>>>> stg_newArrayzh in rts/PrimOps.cmm doesn't appear to give any indication,
>>>> so this might be a good patch to add.  But I'm curious: what would
>>>> allocating Array#s of size 0 do? Null pointers? That sounds dangerous...
>>> I would imagine that a zero sized array would be a StgArrPtrs header
>>> with its size field set to 0. It's not a very useful thing to have, I
>>> admit. If someone (Simon?) can confirm that we don't intend to support
>>> zero-length array I'll push a patch that adds a comment.
>>> Johan
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