You're dereferencing a "super pointer" to get to a "pointer", hence * not
&. You can't "go back" because the local/global<T> represents an
"reference count" to the object which must be known to the JS runtime.
As for p0 and p1, have you tried setting slot to a fixed string value
before using it as a key for storing/lookup? I don't know what the
expected behavior of using an empty value as a key into an object is.
These are all just guesses - if someone else answers differently, I'm
probably wrong.
On Thursday, June 21, 2018 at 5:07:50 AM UTC-7, Gonzalo Diethelm wrote:
>
> Note to self: this might be related to Local<Object> vs Global<Object> (or
> Persistent<Object>? so many names...)
>
> Need to look into that.
>
> On Thursday, June 21, 2018 at 7:58:37 AM UTC+2, Gonzalo Diethelm wrote:
>>
>> I run the following JS code in the Chrome console:
>>
>> // Version 67.0.3396.87 (Official Build) (64-bit)
>>
>> var x = [1, 2, {"foo": 11}];
>> x[2].bar = x;
>>
>> Now from C++ code, I get ahold of x as a Local<Object>, and wish to
>> traverse the whole structure; for the sake of the example, let's say I am
>> converting it into serialized data (I know I can use JSON.stringify() to do
>> this, serializing is just an example to clarify ideas). My question is,
>> how can I keep track of the nodes in the structure that I have already
>> seen, and their associated serialized value, so that I can avoid an
>> infinite traversal?
>>
>> It seems to me doing this would require a way to get a unique identity
>> for each node, so that the C++ code can do something similar to this:
>>
>> typedef map<NodeId, NodeData> NodeMap;
>> NodeMap seen;
>> ...
>> Local<Object> node = current.GetNextChild();
>> NodeId id = node.GetUniqueId();
>> NodeMap::iterator k = seen.find(id);
>> NodeData data;
>> if (k != seen.end()) {
>> // node already seen, reuse its serialization
>> data = k->first;
>> } else {
>> // first time we see node, serialize and remember
>> data = node.Serialize(); // recurses
>> seen[id] = data;
>> }
>>
>> The specific question is: what type could be NodeId, and how do I get the
>> equivalent of GetUniqueId()?
>>
>> I am very tempted to ask for a way to get a raw void* to each node, but I
>> guess any way of doing this is fine, as long as I can get a unique id that
>> is stable while I'm traversing the data. For these reasons,
>> GetIdentityHash() does not seem to fit the bill: "*The return value will
>> never be 0. Also, it is not guaranteed to be unique.*"
>>
>> Incidentally, If I try to use JSON.stringify for my data, I get this:
>>
>> JSON.stringify(x)
>> VM170:1 Uncaught TypeError: Converting circular structure to JSON
>> at JSON.stringify (<anonymous>)
>> at <anonymous>:1:6
>>
>> This is taken care of here in the V8 code:
>>
>> JsonStringifier::Result JsonStringifier::StackPush(Handle<Object> object)
>> {
>> ...
>> // member stack_ is: Handle<JSArray> stack_;
>> int length = Smi::ToInt(stack_->length());
>> FixedArray* elements = FixedArray::cast(stack_->elements());
>> for (int i = 0; i < length; i++) {
>> FixedArray* elements = FixedArray::cast(stack_->elements());
>> if (elements->get(i) == *object) {
>> // boom
>> }
>> }
>> }
>>
>> So, operator*() in a Handle<Object> gives me a unique id? Which is the
>> type for this? Can I store that in a C++ map? Is it stable (enough)?
>>
>> Thanks!
>>
>
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