On Thursday, 12 July 2012 at 08:59:46 UTC, Don Clugston wrote:
On 12/07/12 06:15, Andrei Alexandrescu wrote:
Required reading prior to this: http://goo.gl/eXpuX
You destroyed, we listened.
I think Christophe makes a great point. We've been all
thinking inside
the box but we should question the very existence of the box.
Once the
necessity of opCmp, opEquals, toHash, toString is being
debated, we get
to some interesting points:
1. Polymorphic comparisons for objects has problems even
without
considering interaction with qualifiers. I wrote quite a few
pages about
that in TDPL, which add to a lore grown within the Java
community.
2. C++ has very, very successfully avoided the necessity of
planting
polymorphic comparisons in base classes by use of templates.
The issue
is template code bloat. My impression from being in touch with
the C++
community for a long time is that virtually nobody even talks
about code
bloat anymore. For whatever combination of industry and market
forces,
it's just not an issue anymore.
3. opCmp, opEquals, and toHash are all needed primarily for
one thing:
built-in hashes. (There's also use of them in the moribund
.sort
method.) The thing is, the design of built-in hashes predates
the
existence of templates. There are reasons to move to
generic-based
hashes instead of today's runtime hashes (such as the
phenomenal success
of templated containers in C++), so it can be argued that
opCmp,
opEquals, and toHash exist for reasons that are going extinct.
4. Adding support for the likes of logical constness is
possible, but
gravitates between too lax and onerously complicated. Walter
and I don't
think the aggravation is justified.
There are of course more angles and considerations. Walter and
I
discussed such for a while and concluded we should take the
following
route:
1. For the time being, rollback the changes. Kenji, could you
please do
the honors? There's no need to undo everything, only the key
parts in
object.d. Apologies for having to undo your work!
2. Investigate a robust migration path from the current use of
opCmp,
opEquals, toHash (we need to also investigate toString) to a
world in
which these methods don't exist in Object. In that world,
associative
arrays would probably be entirely generic. Ideally we should
allow
existing code to still work, while at the same time fostering
a better
style for new code.
What say you?
Andrei
Well:
* having opCmp() defined for all objects is just plain weird.
* toString() is a poor design anyway.
But we'd need to be very careful, this is a very disruptive
change.
I don't find them that weird, because many OO languages do have
them.
But I am fine with the design that feels better in D.
--
Paulo
