Can't add a Persistent<Function> to vector<Persistent<Function>> - c++

Question

I'm migrating from v8 3.x to 4.y and I'm having problems with one of the functions defined in one of my header file.
//JavascriptBase.h
namespace Company {
class Base {
protected:
void registerHandler(v8::Persistent<v8::Function>& func) {
user_functions_.push_back(func);
}
private:
std::vector<v8::Persistent<v8::Function>> user_functions_;
}
}
When I try to compile I get the following errors:
third-party2/v8/4.7.39/gcc-4.8.1-glibc-2.17-fb/281a9e6/include/v8.h:667:53: error: assigning to 'v8::Object *volatile' from incompatible type 'v8::Primitive *'
while (false) { *(static_cast<O* volatile*>(0)) = static_cast<Primitive*>(0); };
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
third-party2/v8/4.7.39/gcc-4.8.1-glibc-2.17-fb/281a9e6/include/v8.h:663:5: note: in instantiation of function template specialization 'v8::NonCopyablePersistentTraits<v8::Function>::Uncompilable<v8::Object>' requested here
Uncompilable<Object>();
^
third-party2/v8/4.7.39/gcc-4.8.1-glibc-2.17-fb/281a9e6/include/v8.h:7175:6: note: in instantiation of function template specialization 'v8::NonCopyablePersistentTraits<v8::Function>::Copy<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >' requested here
M::Copy(that, this);
^
third-party2/v8/4.7.39/gcc-4.8.1-glibc-2.17-fb/281a9e6/include/v8.h:729:5: note: in instantiation of function template specialization 'v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >::Copy<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >' requested here
Copy(that);
^
third-party2/libgcc/4.8.1/gcc-4.8.1-glibc-2.17-fb/8aac7fc/include/c++/4.8.1/ext/new_allocator.h:120:23: note: in instantiation of member function 'v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >::Persistent' requested here
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
third-party2/libgcc/4.8.1/gcc-4.8.1-glibc-2.17-fb/8aac7fc/include/c++/4.8.1/bits/alloc_traits.h:254:8: note: in instantiation of function template specialization '__gnu_cxx::new_allocator<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > >::construct<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >, const v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > &>' requested here
{ __a.construct(__p, std::forward<_Args>(__args)...); }
^
third-party2/libgcc/4.8.1/gcc-4.8.1-glibc-2.17-fb/8aac7fc/include/c++/4.8.1/bits/alloc_traits.h:393:4: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > > >::_S_construct<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >, const v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > &>' requested here
{ _S_construct(__a, __p, std::forward<_Args>(__args)...); }
^
third-party2/libgcc/4.8.1/gcc-4.8.1-glibc-2.17-fb/8aac7fc/include/c++/4.8.1/bits/stl_vector.h:905:21: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > > >::construct<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >, const v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > &>' requested here
_Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
^
./Company/JavaScriptBase.h:84:21: note: in instantiation of member function 'std::vector<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> >, std::allocator<v8::Persistent<v8::Function, v8::NonCopyablePersistentTraits<v8::Function> > > >::push_back' requested here
user_functions_.push_back(func);
^
1 error generated.
I've done some googling and found that Persistent objects aren't assignable but I'm not sure what to do with this information. Any help would be appreciated.

Answer 1

If they aren't assignable then you (obviously) can't assign them. And since std::vector<> relies on copying values using the assignment operator, your approach won't work.
You can however store pointers to them instead, since copying pointers of anything is well defined.

Answer 2

You can make a copyable persistent with this "typedef"
using CopyablePersistent = v8::Persistent<T, v8::CopyablePersistentTraits<T>>;
This assumes it's inside a templated class, but you can make the T whatever you want.
edit: apparently this is a "very bad" thing to do, but I don't know why.