[sv-ec] Mantis 2380 - array assignment compatibility

I think  the un-addressed ballot items 33, 34, 56 (Mantis 2380)
may well come back to haunt us, so it's probably as well to be 
prepared for it.

We are in a bit of a mess with array assignment compatibility.
There is plenty of text in 7.6 saying that unpacked arrays
of any kind (fixed-size, queue, dynamic) should be assignment
compatible if they are of the same shape and their elements 
are of **assignment compatible** type, and I would strongly 
argue that users would reasonably expect that to be true.
On the other hand, there is also a specific statement in
7.6 that fixed-size unpacked arrays are assignment
compatible with one another only if their shapes are the
same and their elements are of **equivalent** type.  I have
argued before, and restate here, that I see no sensible
reason for the element-equivalence requirement.  If an 
implementation wishes to use memory block-copy to copy
one unpacked array to another, it is free to do so if
it can statically determine that the elements are 
of equivalent type.  If they are not, it would be a
great courtesy to users for the implementation to do 
the element-by-element copy, which the language does 
not readily permit users to code in a general way.

I would therefore very much like to rewrite 7.6 to redefine
assignment compatibility of unpacked arrays so that the
elements need only be assignment-compatible, not equivalent.
This would require a few other very minor LRM changes:
a cross-reference from the main entry on assignment 
compatibility (6.22.3) to the new 7.6 text, a few small
fixes elsewhere.  I'm happy to write up a proposal if
people agree this is sensible.  But I also understand
that there may be some vendor push-back against this.

What do you think?

Thanks
-- 
Jonathan Bromley
Consultant

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