WeakObjectIdDict & more general dicts

[mauro3]

I'm looking for a weak object-id dict for JuliaLang/julia/pull/5572. There is one implementation here: JuliaLang/julia/issues/3002. One feature needed is that it also works with immutable keys.

A potentially general way to go about this is to add two features to HashDict:

• possibility of key transformation: For this case it would be key -> WeakRef(key). (This is essentially what the add_weak_key function in Base does.)
• possibility of adapting the hashindex function. For object-id it would look:
  hashindex(key, sz) = (int(hash(object_id(key))) & (sz-1)) + 1

I'm not sure how to go about this: The usual way would be to use dispatch on the functions: hashindex(::Associative, key, sz) = (int(hash(key)) & (sz-1)) + 1. However, because HashDict is wrapped this does not work (or at least I cannot see how). Any ideas on how to go about this?

[kmsquire]

For everything that wraps HashDict, we delegate most functions to the wrapped dictionary through the @delegate macro (e.g., https://github.com/JuliaLang/DataStructures.jl/blob/master/src/ordereddict.jl#L38-L41). I think this should work here as well. Do you see a reason why that might not be true?

[mauro3]

Tnx for looking into this. The method concerned here is hashindex which is internal to HashDict. Thus I don't think delegating works. If I make a new type MyDict which wraps HashDict, the internal hashindex still gets called, even if redefined as something like this hashindex(::Associative, key, sz) and hashindex(::MyDict, key, sz) because the underlying datatype is still HashDict.

[kmsquire]

Okay. Are you importing hashindex() before overriding for HashDict and
MyDict? Do you have any code you can share in a gist?

On Wednesday, June 18, 2014, Mauro notifications@github.com wrote:

Tnx for looking into this. The method concerned here is hashindex which
is internal to HashDict. Thus I don't think delegating works. If I make a
new type MyDict which wraps HashDict, the internal hashindex still gets
called, even if redefined as something like this hashindex(::Associative,
key, sz) and hashindex(::MyDict, key, sz) because the underlying datatype
is still HashDict.

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[mauro3]

At the moment I just copy-pasted Dict and modified it, which works but I think it could be done better:
https://github.com/mauro3/julia/blob/metadata/base/dict.jl#L775-L1186

There should be a way to unify all the hash-based dicts including this one. You have been pursuing this quest for a wee while, maybe you got some insights on how to solve this more generally?

[oxinabox]

I think this is stalled and can be closed?