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Improve custom holder support (#607)

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* Abstract away some holder functionality (resolve #585)

Custom holder types which don't have `.get()` can select the correct
function to call by specializing `holder_traits`.

* Add support for move-only holders (fix #605)
This commit is contained in:
Dean Moldovan
2017-01-31 17:05:44 +01:00
committed by Wenzel Jakob
parent f7f5bc8e37
commit ec009a7ca2
6 changed files with 113 additions and 36 deletions
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56
include/pybind11/cast.h
View File

@@ -402,6 +402,13 @@ public:
make_copy_constructor(src), make_move_constructor(src));
}
static handle cast_holder(const itype *src, const void *holder) {
return type_caster_generic::cast(
src, return_value_policy::take_ownership, {},
src ? &typeid(*src) : nullptr, &typeid(type),
nullptr, nullptr, holder);
}
template <typename T> using cast_op_type = pybind11::detail::cast_op_type<T>;
operator itype*() { return (type *) value; }
@@ -636,17 +643,6 @@ protected:
bool success = false;
};
template <typename type, typename deleter> class type_caster<std::unique_ptr<type, deleter>> {
public:
static handle cast(std::unique_ptr<type, deleter> &&src, return_value_policy policy, handle parent) {
handle result = type_caster_base<type>::cast(src.get(), policy, parent);
if (result)
src.release();
return result;
}
static PYBIND11_DESCR name() { return type_caster_base<type>::name(); }
};
template <> class type_caster<std::wstring> {
public:
bool load(handle src, bool) {
@@ -837,8 +833,16 @@ protected:
std::tuple<make_caster<Tuple>...> value;
};
/// Helper class which abstracts away certain actions. Users can provide specializations for
/// custom holders, but it's only necessary if the type has a non-standard interface.
template <typename T>
struct holder_helper {
static auto get(const T &p) -> decltype(p.get()) { return p.get(); }
};
/// Type caster for holder types like std::shared_ptr, etc.
template <typename type, typename holder_type> class type_caster_holder : public type_caster_base<type> {
template <typename type, typename holder_type>
struct copyable_holder_caster : public type_caster_base<type> {
public:
using base = type_caster_base<type>;
using base::base;
@@ -917,7 +921,7 @@ public:
template <typename T = holder_type, detail::enable_if_t<std::is_constructible<T, const T &, type*>::value, int> = 0>
bool try_implicit_casts(handle src, bool convert) {
for (auto &cast : typeinfo->implicit_casts) {
type_caster_holder sub_caster(*cast.first);
copyable_holder_caster sub_caster(*cast.first);
if (sub_caster.load(src, convert)) {
value = cast.second(sub_caster.value);
holder = holder_type(sub_caster.holder, (type *) value);
@@ -940,10 +944,8 @@ public:
#endif
static handle cast(const holder_type &src, return_value_policy, handle) {
return type_caster_generic::cast(
src.get(), return_value_policy::take_ownership, handle(),
src.get() ? &typeid(*src.get()) : nullptr, &typeid(type),
nullptr, nullptr, &src);
const auto *ptr = holder_helper<holder_type>::get(src);
return type_caster_base<type>::cast_holder(ptr, &src);
}
protected:
@@ -952,7 +954,25 @@ protected:
/// Specialize for the common std::shared_ptr, so users don't need to
template <typename T>
class type_caster<std::shared_ptr<T>> : public type_caster_holder<T, std::shared_ptr<T>> { };
class type_caster<std::shared_ptr<T>> : public copyable_holder_caster<T, std::shared_ptr<T>> { };
template <typename type, typename holder_type>
struct move_only_holder_caster {
static handle cast(holder_type &&src, return_value_policy, handle) {
auto *ptr = holder_helper<holder_type>::get(src);
return type_caster_base<type>::cast_holder(ptr, &src);
}
static PYBIND11_DESCR name() { return type_caster_base<type>::name(); }
};
template <typename type, typename deleter>
class type_caster<std::unique_ptr<type, deleter>>
: public move_only_holder_caster<type, std::unique_ptr<type, deleter>> { };
template <typename type, typename holder_type>
using type_caster_holder = conditional_t<std::is_copy_constructible<holder_type>::value,
copyable_holder_caster<type, holder_type>,
move_only_holder_caster<type, holder_type>>;
template <typename T, bool Value = false> struct always_construct_holder { static constexpr bool value = Value; };

30
include/pybind11/pybind11.h
View File

@@ -1212,24 +1212,22 @@ private:
}
}
/// Initialize holder object, variant 2: try to construct from existing holder object, if possible
template <typename T = holder_type,
detail::enable_if_t<std::is_copy_constructible<T>::value, int> = 0>
static void init_holder_helper(instance_type *inst, const holder_type *holder_ptr, const void * /* dummy */) {
if (holder_ptr) {
new (&inst->holder) holder_type(*holder_ptr);
inst->holder_constructed = true;
} else if (inst->owned || detail::always_construct_holder<holder_type>::value) {
new (&inst->holder) holder_type(inst->value);
inst->holder_constructed = true;
}
static void init_holder_from_existing(instance_type *inst, const holder_type *holder_ptr,
std::true_type /*is_copy_constructible*/) {
new (&inst->holder) holder_type(*holder_ptr);
}
/// Initialize holder object, variant 3: holder is not copy constructible (e.g. unique_ptr), always initialize from raw pointer
template <typename T = holder_type,
detail::enable_if_t<!std::is_copy_constructible<T>::value, int> = 0>
static void init_holder_helper(instance_type *inst, const holder_type * /* unused */, const void * /* dummy */) {
if (inst->owned || detail::always_construct_holder<holder_type>::value) {
static void init_holder_from_existing(instance_type *inst, const holder_type *holder_ptr,
std::false_type /*is_copy_constructible*/) {
new (&inst->holder) holder_type(std::move(*const_cast<holder_type *>(holder_ptr)));
}
/// Initialize holder object, variant 2: try to construct from existing holder object, if possible
static void init_holder_helper(instance_type *inst, const holder_type *holder_ptr, const void * /* dummy */) {
if (holder_ptr) {
init_holder_from_existing(inst, holder_ptr, std::is_copy_constructible<holder_type>());
inst->holder_constructed = true;
} else if (inst->owned || detail::always_construct_holder<holder_type>::value) {
new (&inst->holder) holder_type(inst->value);
inst->holder_constructed = true;
}