Support enable_shared_from_this #212
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wjakob
reviewed
May 12, 2023
| slightly larger than bindings for a class that doesn't, as nanobind | ||
| must produce type-specific code to implement the above behaviors. | ||
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| .. warning:: The ``shared_from_this()`` method will only work when there |
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Doesn't the body (The [..]) need to start on the line following the warning:: block? Maybe I just misremember.
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I've always written them this way, and the docs look correct when built. I think the only requirement is that continuation lines line up with the 'w' in warning::.
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| Replacing shared pointers with :ref:`intrusive reference counting | ||
| <intrusive>` fixes this limitations. | ||
| enable_shared_from_this |
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Awesome, this is really clear documentation of the nuances of this feature 👍
| d.flags |= (uint32_t) detail::type_flags::has_shared_from_this; | ||
| d.keep_shared_from_this_alive = [](PyObject *self) noexcept { | ||
| if (auto sp = inst_ptr<T>(self)->weak_from_this().lock()) { | ||
| detail::keep_alive(self, new auto(std::move(sp)), |
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Per discussion in #183, this is not actually dangerous, although it does have some caveats (which I think I've thoroughly documented).
This turned out better than I thought it would: it is unexpectedly possible to support the feature where returning a raw pointer whose
enable_shared_from_thissubobject knows about a shared_ptr creates a Python object that shares ownership with that shared_ptr, without requiring#include <memory>anywhere in nanobind that doesn't already have it.Size impact:
nb_type.cpp.oincreases by 148 bytes. Use ofstd::shared_ptr<T>in non-enable_shared_from_thiscases actually gets smaller; we were previously instantiating a deleter forPyObject*by mistake, and now we're not.