There is no technical reason for not storing templates in internal fields. They're very similar to Externals in that regard: they're safe to store in objects as long as they can only be accessed from C++.
The reason they're in a hierarchy of their own is that getting them mixed up with ordinary values is in most cases dangerous and it seemed safest to use the type system to separate them completely. The best solution would probably be to allow internal object fields to hold Handle<Data>s rather than Handle<Value>s since that is one case where mixing the two is always safe. On Mon, Jun 8, 2009 at 11:08 PM, Matthias Ernst<[email protected]> wrote: > > So I've patched my local copy of v8 to support "Data" as internal > object fields instead of "Value". > It required changing all the v8::XX::Cast(Value *) methods to > Cast(Data *) and adding an ObjectTemplate::Cast(Data *) like so: > >> ObjectTemplate* ObjectTemplate::Cast(v8::Data* that) { >> if (IsDeadCheck("v8::ObjectTemplate::Cast()")) return 0; >> i::Handle<i::Object> obj = Utils::OpenHandle(that); >> ApiCheck(obj->IsObjectTemplateInfo(), >> "v8::ObjectTemplate::Cast()", >> "Could not convert to ObjectTemplate"); >> return static_cast<ObjectTemplate*>(that); >> } > > With that, building the structure outlined before seems to work fine. > I'd still be interested to know whether this is kosher. > > Matthias > > On Mon, Jun 8, 2009 at 12:12 PM, Matthias Ernst<[email protected]> > wrote: >> Hi, >> >> Synopsis: I'm wondering how I can have a v8::Object point to a v8::Template. >> >> Here's what I'm doing: I'm hacking away at a protocol buffer wrapper. >> >> In my design, every protocol message type (represented by a >> proto2::Descriptor*) is mapped to an ObjectTemplate. >> Each property of the message type becomes an Accessor that calls back into >> C++. The Accessor's "data" contains the proto2::FieldDescriptor and -in the >> case of a sub-message- the object template used to wrap that submessage's >> type. >> >> So for a message Outer { Inner inner; }, the layout I'd like to have is as >> such: >> ObjectTemplate"Outer" { >> Accessor"inner" : { >> Callback"read and wrap submessage", >> Data: Handle->Object{ >> External<FieldDescriptor"inner" *>, >> Handle->ObjectTemplate"Inner" -> ... <= ******* >> } >> } >> } >> >> I would like the whole structure to be managed by the V8 GC (the proto >> descriptors are static data), i.e. I'd like the inner ObjectTemplates to be >> GC'ed once I drop the outer one. >> >> However, and here's my actual problem, I cannot get the callback data to >> refer to the inner v8::ObjectTemplate (*****), because the latter does not >> extend v8::Value but only v8::Data. The only way I can imagine is using an >> External wrapping a Persistent* but that would defeat the GC. >> >> So, is there a fundamental reason why "Data" cannot be used even as an >> internal field of an Object? >> I see that internally, in objects.h, an AccessorInfo's "Data" is not >> required to be a JSObject but just an Object. >> >> Would horrible things happen if I coerced a Handle<ObjectTemplate> to be a >> Handle<Value> and store it as internal fields of the callback Data? Could we >> change Object::Set/GetInternalField to use Handle<Data>? >> >> Thx >> Matthias >> >> > > > > --~--~---------~--~----~------------~-------~--~----~ v8-users mailing list [email protected] http://groups.google.com/group/v8-users -~----------~----~----~----~------~----~------~--~---
