Why are opEquals/opCmp arguments not in or const for Objects?

[Peter Williams]

On Monday, 18 March 2013 at 01:05:25 UTC, Jonathan M Davis wrote:
> On Monday, March 18, 2013 00:53:52 Stewart Gordon wrote:
>> Why would some class want to implement these methods in a way 
>> that alters
>> the object?
>
> Because const in D is physical const, not logical const. So, 
> for instance,
> const prevents caching. And it's quite possible that a type 
> which really cared
> about efficiency would cache the calculated value for toHash. 
> Make toHash const
> would make that impossible. Another possible problem would be 
> lazy
> initialization. If opEquals is const, then lazy initialization 
> becomes
> impossible.
>
> We've discussed this on a number of occasions, and it's clear 
> that forcing
> these functions to be const is a major problem, and yet they do 
> need to be
> const for them to work with const objects. What was finally 
> decided during the
> last big discussion on this a few months back was that we would 
> remove
> opEqulas, opCmp, toHash, and toString from Object. They don't 
> need to be
> there. As long as everything in the runtime which deals with 
> them is
> templated, then there's no technical reason why Object would 
> need them. D
> isn't Java where we have containers of Object or anything like 
> that. Putting
> them on Object just restricts us.
>
> So, once all of those functions are removed from Object, 
> derived types can
> then define them with whatever attributes they want. The only 
> thing you lose is
> the ability to compare Objects directly, which is not necessary 
> in D and is
> arguably a bad idea anyway.
>
> The work on this conversion hasn't been done yet, and a 
> transition plan will
> have to be put in place to minimize code breakage, but that's 
> what was decided
> on as the solution to the issues with const and Object's 
> functions.
>
> - Jonathan M Davis

Am I right in thinking that removal of these methods from Object 
will mean that it will no longer be necessary for the the 
argument to be of type Object and that the need for casting in 
the implementation will go away?

Peter