Sorry for my bad language. I've not written much about immutable structures
before so old phraseology keeps coming in inappropriately.
The structures are immutable. A change results in a new tree with only the
nodes which are changed (and their parent nodes) replaced. But the key
property here is that deserialization and serialization operations which
are performed on these trees are done in place, without making any new
nodes--thanks to the magic of atoms. So for example, if several threads are
accessing the same tree instance, they all share the deserialized values
while any changes to the tree contents results in new tree instances. I.E.
It is done right, to the best of my ability. (Extra eyeballs on the code
always being appreciated, of course!)
Now I'm sorry for having been so terse and ambiguous. I need practice
talking about this stuff. So your questions are appreciated twice over! :-)
On Thursday, October 1, 2015 at 4:41:33 PM UTC-4, Nathan Davis wrote:
>
>
>
> On Thursday, October 1, 2015 at 2:58:15 PM UTC-5, William la Forge wrote:
>>
>> A value can have more than one form or implementation. For example, a
>> String and a char array may both represent the same value. Most objects,
>> for example, can be serialized. Changing the form of a value then is not a
>> change of value. This is the idea behind lazy deserialization /
>> reserialization.
>>
>>
>> We can represent a data structure as a tree, where the values in the tree
>> can be either the immutable value of the object or a read-only ByteBuffer
>> holding the serialized form of the value, or both. Both forms can be held
>> by nodes using atoms, so the form of the values can be changed without
>> having to create a new tree. The value remains unchanged and the tree can
>> be safely shared between threads.
>>
>
> I think we are on the same page to this point.
>
>
>> Lazy deserialization comes after loading a map or vector from a
>> ByteBuffer. Initially only the root exists, which holds only the
>> ByteBuffer. As you access and alter the contents of the map or vector, the
>> portions of the tree which are accessed are deserialized.
>>
>
> This is where I get confused. Are aatrees persistent structures (in the
> functional programming sense, like Clojure's data structures) whose values
> cannot be changed (although their internal representation ("form") may
> change), or are they mutable? If they are persistent, what do you mean by
> "alter the contents"?
>
> Nathan Davis
>
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