On Tue, Oct 13, 2020 at 3:37 PM Elling B <elling.bjas...@gmail.com> wrote:
>
> I found this helper method in a tutorial a couple of days ago.
>
> It reinterpret casts a v8::Persistent to a v8::Local, with the intended use
> of calling V8 API functions that require a local handle to a context, without
> actually having to create a new v8::Local each time:
>
> template <class TypeName>
> inline v8::Local<TypeName> ToLocal(const v8::Persistent<TypeName>& persistent)
> {
> return
> *reinterpret_cast<v8::Local<TypeName>*>(const_cast<v8::Persistent<TypeName>*>(&persistent));
> }
>
> I'm new to V8, so I find myself wondering if it's safe or not. Or if it can
> be safe in some cases.
Full disclosure: that StrongPersistentToLocal() helper from the
article is my code. I introduced that trick in the Node.js code base
years ago and looks like people copied it. Mea culpa. :broken_smile:
So, it works, but it's not particularly safe. Caveats:
- don't use it on weakly persistent handles, only strong ones, and
- don't call .Reset() while the Local is still in use
Node.js (ab)uses it for performance reasons but most of the time you
should just use `Local<Value>::New(isolate, persistent)`.
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