Cloning in D

[Jacob Carlborg]

On 2010-09-06 16:12, Andrei Alexandrescu wrote:
> On 09/05/2010 10:15 PM, dsimcha wrote:
>> I've started playing around with Orange a little to see whether it
>> would meet
>> D's cloning needs. IMHO one must-have feature for proper cloning that
>> truly
>> "just works" is full aliasing preservation.
>
> What do you mean by aliasing preservation? I'd think you want no
> aliasing between the clone and the original. (Perhaps you mean that the
> object graph of the clone and original look the same?)
>
> First off, let's see what cloning methods we have:
>
> 1. We know how to clone built-in types except pointers. (Arrays are
> cloned by duplicating the array proper and cloning each element.)
>
> 2. Structs can be cloned with either this(this) or by cloning each of
> their fields.
>
> 3. For classes we can define a conventional method/interface, e.g.
> clone/Cloneable.
>
> Now, given some arbitrary value v, we know how to obtain a clone of it
> by applying the rules above. The problem is, there are two opaque calls:
> this(this) for structs and obj.clone() for classes. If improperly
> implemented, the whole thing comes unglued. The problem is the standard
> library (and others) must rely on correct deep cloning without being
> able to check it.
>
> Although it's difficult to implement deep cloning, it's relatively easy
> to _verify_ it. So I'm thinking, a generic deepdup() routine would apply
> cloning per the rules above and then would verify that opaque calls
> obj.clone() and this(this) did not produce any aliasing.
>
> Bottom line, this clarifies we need dynamic field information for
> classes. Otherwise we wouldn't be able to "see" through polymorphism.
>
>
> Andrei

That would be getMembers in ClassInfo, but it doesn't currently work: 
issue 2844. It also returns an empty array, I think, can't find the 
ticket for that though. We also need to be able to set and get the value 
of a field, don't know if this would be possible by using the offset 
field in the MemberInfo_field class. This is also needed for a 
completely transparent serialization implementation (i.e. the user 
doesn't have to implement or register any methods/functions).

-- 
/Jacob Carlborg