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Factoring out make_constructor from type_caster_base (for reuse under PR #2672). #2798

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Factoring out make_constructor from type_caster_base (for reuse under PR #2672). #2798

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5e3a4cb
Factoring out make_constructor from type_caster_base (for reuse under…
Jan 16, 2021
7281e03
Explicit use of make_constructor functions, instead of using (multipl…
Jan 17, 2021
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49 changes: 26 additions & 23 deletions include/pybind11/cast.h
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Original file line number Diff line number Diff line change
Expand Up @@ -816,6 +816,30 @@ template <typename Container> struct is_copy_assignable<Container, enable_if_t<a
template <typename T1, typename T2> struct is_copy_assignable<std::pair<T1, T2>>
: all_of<is_copy_assignable<T1>, is_copy_assignable<T2>> {};

// Helper for type_caster_base.
struct make_constructor {
using Constructor = void *(*)(const void *);

/* Only enabled when the types are {copy,move}-constructible *and* when the type
does not have a private operator new implementation. */
template <typename T, typename = enable_if_t<is_copy_constructible<T>::value>>
static auto make_copy_constructor(const T *x) -> decltype(new T(*x), Constructor{}) {
return [](const void *arg) -> void * {
return new T(*reinterpret_cast<const T *>(arg));
};
}

template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
static auto make_move_constructor(const T *x) -> decltype(new T(std::move(*const_cast<T *>(x))), Constructor{}) {
return [](const void *arg) -> void * {
return new T(std::move(*const_cast<T *>(reinterpret_cast<const T *>(arg))));
};
}

static Constructor make_copy_constructor(...) { return nullptr; }
static Constructor make_move_constructor(...) { return nullptr; }
};

PYBIND11_NAMESPACE_END(detail)

// polymorphic_type_hook<itype>::get(src, tinfo) determines whether the object pointed
Expand Down Expand Up @@ -905,7 +929,8 @@ template <typename type> class type_caster_base : public type_caster_generic {
auto st = src_and_type(src);
return type_caster_generic::cast(
st.first, policy, parent, st.second,
make_copy_constructor(src), make_move_constructor(src));
make_constructor::make_copy_constructor(src),
make_constructor::make_move_constructor(src));
}

static handle cast_holder(const itype *src, const void *holder) {
Expand All @@ -919,28 +944,6 @@ template <typename type> class type_caster_base : public type_caster_generic {

operator itype*() { return (type *) value; }
operator itype&() { if (!value) throw reference_cast_error(); return *((itype *) value); }

protected:
using Constructor = void *(*)(const void *);

/* Only enabled when the types are {copy,move}-constructible *and* when the type
does not have a private operator new implementation. */
template <typename T, typename = enable_if_t<is_copy_constructible<T>::value>>
static auto make_copy_constructor(const T *x) -> decltype(new T(*x), Constructor{}) {
return [](const void *arg) -> void * {
return new T(*reinterpret_cast<const T *>(arg));
};
}

template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
static auto make_move_constructor(const T *x) -> decltype(new T(std::move(*const_cast<T *>(x))), Constructor{}) {
return [](const void *arg) -> void * {
return new T(std::move(*const_cast<T *>(reinterpret_cast<const T *>(arg))));
};
}

static Constructor make_copy_constructor(...) { return nullptr; }
static Constructor make_move_constructor(...) { return nullptr; }
};

template <typename type, typename SFINAE = void> class type_caster : public type_caster_base<type> { };
Expand Down