What's the difference between v8::Global and v8::Persistent?
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tbl...@icloud.com
Oct 1, 2016, 9:33:33 PM10/1/16
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The documentation comments say Persistent "allows copy and assignment", and Global has "move semantics". What exactly does that mean?
Thanks
~Theodore
Zac Hansen
Oct 1, 2016, 9:53:57 PM10/1/16
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They are synonyms. Just like Local and Handle.
Theodore Dubois
Oct 1, 2016, 9:56:07 PM10/1/16
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Well, Handle is a typedef to Local, but Global is not a typedef to Persistent. Global and Persistent are different subclasses of PersistentBase. So there must be some difference between them.
~Theodore
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Zac Hansen
Oct 1, 2016, 10:29:46 PM10/1/16
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Ah, UniquePersistent is what is the same as a Global.
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Theodore Dubois
Oct 1, 2016, 10:32:52 PM10/1/16
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What exactly does that mean? Does that mean this:
Persistent<String> string(String::NewFromUtf8(isolate, “string”, NewStringType::kNormal).ToLocalChecked());
Persistent<String string2 = string;
would result in two different string objects, and using Global instead would result in two handles to the same object?
~Theodore
> On Oct 1, 2016, at 7:29 PM, Zac Hansen <xax...@gmail.com> wrote:
>
> Ah, UniquePersistent is what is the same as a Global.
>
> https://docs.google.com/document/d/1g8JFi8T_oAE_7uAri7Njtig7fKaPDfotU6huOa1alds/edit
>
> • Rename UniquePersistent to Global and give it full move semantics: CL CL
>
> Looks like Persistent is copyable?
>
> On Sat, Oct 1, 2016 at 6:55 PM, Theodore Dubois <tbl...@icloud.com> wrote:
> Well, Handle is a typedef to Local, but Global is not a typedef to Persistent. Global and Persistent are different subclasses of PersistentBase. So there must be some difference between them.
>
> ~Theodore
>
> > On Oct 1, 2016, at 6:53 PM, Zac Hansen <xax...@gmail.com> wrote:
> >
> > They are synonyms. Just like Local and Handle.
> >
> > On Saturday, October 1, 2016 at 6:33:33 PM UTC-7, tbl...@icloud.com wrote:
> > The documentation comments say Persistent "allows copy and assignment", and Global has "move semantics". What exactly does that mean?
> >
> > Thanks
> > ~Theodore
> >
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Persistent<String> string(String::NewFromUtf8(isolate, “string”, NewStringType::kNormal).ToLocalChecked());
Persistent<String string2 = string;
would result in two different string objects, and using Global instead would result in two handles to the same object?
~Theodore
> On Oct 1, 2016, at 7:29 PM, Zac Hansen <xax...@gmail.com> wrote:
>
> Ah, UniquePersistent is what is the same as a Global.
>
> https://docs.google.com/document/d/1g8JFi8T_oAE_7uAri7Njtig7fKaPDfotU6huOa1alds/edit
>
> • Rename UniquePersistent to Global and give it full move semantics: CL CL
>
> Looks like Persistent is copyable?
>
> On Sat, Oct 1, 2016 at 6:55 PM, Theodore Dubois <tbl...@icloud.com> wrote:
> Well, Handle is a typedef to Local, but Global is not a typedef to Persistent. Global and Persistent are different subclasses of PersistentBase. So there must be some difference between them.
>
> ~Theodore
>
> > On Oct 1, 2016, at 6:53 PM, Zac Hansen <xax...@gmail.com> wrote:
> >
> > They are synonyms. Just like Local and Handle.
> >
> > On Saturday, October 1, 2016 at 6:33:33 PM UTC-7, tbl...@icloud.com wrote:
> > The documentation comments say Persistent "allows copy and assignment", and Global has "move semantics". What exactly does that mean?
> >
> > Thanks
> > ~Theodore
> >
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Zac Hansen
Oct 1, 2016, 10:34:00 PM10/1/16
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You get a new object each time you call new. Everything else is just bumping the reference count on that object.
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Theodore Dubois
Oct 1, 2016, 10:38:50 PM10/1/16
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I just noticed that the Global copy constructor sets the other Global’s cell to NULL. I guess that means moving the global around won’t accidentally increment the reference count. That makes sense.
~Theodore
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Zac Hansen
Oct 1, 2016, 10:40:31 PM10/1/16
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Globals are moveable and not copyable, similar to a unique_ptr.
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Theodore Dubois
Oct 1, 2016, 10:41:20 PM10/1/16
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Got it.
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