[Vm-dev] Re: Immutability, newspeak (was: Vm-dev post from jbaptiste.arnaud@gmail.com requires approval)

[Eliot Miranda]

On Tue, Jun 8, 2010 at 9:15 AM, Andreas Raab <andreas.raab at gmx.de> wrote:

>
> On 6/8/2010 7:41 AM, David T. Lewis wrote:
>
>> What do the VM developers think with respect adopting the VM changes?
>> The immutability bit is a scarce resource. Is it OK to allocate it
>> for this purpose or are there likely to be other projects interested
>> in using it for other reasons?
>>
>
> Honestly, I don't thinnk the immutability bit carries its weight here.
> There's some fun stuff you can do with it, for sure, but outside of
> *extremely* specialized applications (oodbs) there will be little to no use
> for it. At least I don't see where you'd make use of immutability in some
> random app that's not a database. If it were essentially free to add it, I
> wouldn't mind (like I said there's fun stuff that one can do) but given that
> we're talking about allocating a header bit I feel that there's just not
> enough mileage we get out of it...
>

It's much more general purpose than OODBs.  Immutable literals and immutable
numerics are very nice to have.  Lazy copying in mutable structures is
useful in general.  A number of other dialects have an immutability bit and
it has carried its weight there. The header bit might as well be used for
something useful.  The argument that it's scarce resource can be used
against any and all uses, and as has been mentioned elsewhere in the thread,
that should be a relatively short-term limitation anyway.

In short, scarce resource issues such as header bits are solvable (by
reimplementing to make more available), immutability is much more generally
useful than OODB interfaces, so (at least form me) this is good use of
something lying fallow.

best
Eliot


> Just my random $.02.
>
> Cheers,
>  - Andreas
>
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