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Allow type_casters to expose temporary dependencies #917

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6 changes: 6 additions & 0 deletions include/pybind11/eigen.h
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Original file line number Diff line number Diff line change
Expand Up @@ -425,6 +425,9 @@ struct type_caster<
// storage order conversion. (Note that we refuse to use this temporary copy when loading an
// argument for a Ref<M> with M non-const, i.e. a read-write reference).
Array copy_or_ref;
// Set when copy_or_ref is a copy, in which case subcaster_keepalive() returns it to keep the
// temporary copy alive when this caster is invoked by a subcaster.
bool is_copy;
public:
bool load(handle src, bool convert) {
// First check whether what we have is already an array of the right type. If not, we can't
Expand Down Expand Up @@ -462,6 +465,7 @@ struct type_caster<
if (!fits || !fits.template stride_compatible<props>())
return false;
copy_or_ref = std::move(copy);
is_copy = true;
}

ref.reset();
Expand All @@ -471,6 +475,8 @@ struct type_caster<
return true;
}

handle subcaster_keepalive() { return is_copy ? (handle) copy_or_ref : handle(); }

operator Type*() { return ref.get(); }
operator Type&() { return *ref; }
template <typename _T> using cast_op_type = pybind11::detail::cast_op_type<_T>;
Expand Down
56 changes: 56 additions & 0 deletions include/pybind11/stl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,27 @@
NAMESPACE_BEGIN(pybind11)
NAMESPACE_BEGIN(detail)

template <typename caster_t, typename = void>
struct subcaster_keepalive_impl { static handle get(caster_t &) { return {}; } };
template <typename caster_t>
struct subcaster_keepalive_impl<caster_t, void_t<decltype(std::declval<caster_t>().subcaster_keepalive())>> {
static handle get(caster_t &caster) { return caster.subcaster_keepalive(); } };
template <typename caster_t>

// Calls caster.subcaster_keepalive() if the caster has it, otherwise returns an empty handle
inline handle subcaster_keepalive(caster_t &caster) { return subcaster_keepalive_impl<caster_t>::get(caster); }



template <typename caster_t>
void append_subcaster_keepalive(object &deps, caster_t &caster) {
if (handle h = subcaster_keepalive(caster)) {
if (!deps) deps = list{};
list deplist(deps);
deplist.append(reinterpret_borrow<object>(h));
}
}

template <typename Type, typename Key> struct set_caster {
using type = Type;
using key_conv = make_caster<Key>;
Expand All @@ -62,6 +83,7 @@ template <typename Type, typename Key> struct set_caster {
key_conv conv;
if (!conv.load(entry, convert))
return false;
append_subcaster_keepalive(deps, conv);
value.insert(cast_op<Key &&>(std::move(conv)));
}
return true;
Expand All @@ -78,6 +100,10 @@ template <typename Type, typename Key> struct set_caster {
}

PYBIND11_TYPE_CASTER(type, _("Set[") + key_conv::name() + _("]"));
private:
object deps;
public:
handle dependency() { return deps; }
};

template <typename Type, typename Key, typename Value> struct map_caster {
Expand All @@ -95,6 +121,8 @@ template <typename Type, typename Key, typename Value> struct map_caster {
if (!kconv.load(it.first.ptr(), convert) ||
!vconv.load(it.second.ptr(), convert))
return false;
append_subcaster_keepalive(deps, kconv);
append_subcaster_keepalive(deps, vconv);
value.emplace(cast_op<Key &&>(std::move(kconv)), cast_op<Value &&>(std::move(vconv)));
}
return true;
Expand All @@ -113,6 +141,10 @@ template <typename Type, typename Key, typename Value> struct map_caster {
}

PYBIND11_TYPE_CASTER(Type, _("Dict[") + key_conv::name() + _(", ") + value_conv::name() + _("]"));
private:
object deps;
public:
handle dependency() { return deps; }
};

template <typename Type, typename Value> struct list_caster {
Expand All @@ -128,6 +160,7 @@ template <typename Type, typename Value> struct list_caster {
value_conv conv;
if (!conv.load(it, convert))
return false;
append_subcaster_keepalive(deps, conv);
value.push_back(cast_op<Value &&>(std::move(conv)));
}
return true;
Expand All @@ -153,6 +186,10 @@ template <typename Type, typename Value> struct list_caster {
}

PYBIND11_TYPE_CASTER(Type, _("List[") + value_conv::name() + _("]"));
private:
object deps;
public:
handle dependency() { return deps; }
};

template <typename Type, typename Alloc> struct type_caster<std::vector<Type, Alloc>>
Expand Down Expand Up @@ -188,6 +225,7 @@ template <typename ArrayType, typename Value, bool Resizable, size_t Size = 0> s
value_conv conv;
if (!conv.load(it, convert))
return false;
append_subcaster_keepalive(deps, conv);
value[ctr++] = cast_op<Value &&>(std::move(conv));
}
return true;
Expand All @@ -206,6 +244,10 @@ template <typename ArrayType, typename Value, bool Resizable, size_t Size = 0> s
}

PYBIND11_TYPE_CASTER(ArrayType, _("List[") + value_conv::name() + _<Resizable>(_(""), _("[") + _<Size>() + _("]")) + _("]"));
private:
object deps;
public:
handle dependency() { return deps; }
};

template <typename Type, size_t Size> struct type_caster<std::array<Type, Size>>
Expand Down Expand Up @@ -246,11 +288,18 @@ template<typename T> struct optional_caster {
if (!inner_caster.load(src, convert))
return false;

if (handle h = subcaster_keepalive(inner_caster))
dep = reinterpret_borrow<object>(h);
value.emplace(cast_op<typename T::value_type &&>(std::move(inner_caster)));
return true;
}

PYBIND11_TYPE_CASTER(T, _("Optional[") + value_conv::name() + _("]"));

private:
object dep;
public:
handle dependency() { return dep; }
};

#if PYBIND11_HAS_OPTIONAL
Expand Down Expand Up @@ -304,6 +353,8 @@ struct variant_caster<V<Ts...>> {
auto caster = make_caster<U>();
if (caster.load(src, convert)) {
value = cast_op<U>(caster);
if (handle h = subcaster_keepalive(caster))
dep = reinterpret_borrow<object>(h);
return true;
}
return load_alternative(src, convert, type_list<Us...>{});
Expand All @@ -329,6 +380,11 @@ struct variant_caster<V<Ts...>> {

using Type = V<Ts...>;
PYBIND11_TYPE_CASTER(Type, _("Union[") + detail::concat(make_caster<Ts>::name()...) + _("]"));

private:
object dep;
public:
handle dependency() { return dep; }
};

#if PYBIND11_HAS_VARIANT
Expand Down