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_enums.h
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95 lines (86 loc) · 3.4 KB
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#ifndef MPL_ENUMS_H
#define MPL_ENUMS_H
#include <pybind11/pybind11.h>
// Extension for pybind11: Pythonic enums.
// This allows creating classes based on ``enum.*`` types.
// This code was copied from mplcairo, with some slight tweaks.
// The API is:
//
// - P11X_DECLARE_ENUM(py_name: str, py_base_cls: str, ...: {str, enum value}):
// py_name: The name to expose in the module.
// py_base_cls: The name of the enum base class to use.
// ...: The enum name/value pairs to expose.
//
// Use this macro to declare an enum and its values.
//
// - py11x::bind_enums(m: pybind11::module):
// m: The module to use to register the enum classes.
//
// Place this in PYBIND11_MODULE to register the enums declared by P11X_DECLARE_ENUM.
// a1 includes the opening brace and a2 the closing brace.
// This definition is compatible with older compiler versions compared to
// #define P11X_ENUM_TYPE(...) decltype(std::map{std::pair __VA_ARGS__})::mapped_type
#define P11X_ENUM_TYPE(a1, a2, ...) decltype(std::pair a1, a2)::second_type
#define P11X_CAT2(a, b) a##b
#define P11X_CAT(a, b) P11X_CAT2(a, b)
namespace p11x {
namespace {
namespace py = pybind11;
// Holder is (py_base_cls, [(name, value), ...]) before module init;
// converted to the Python class object after init.
auto enums = std::unordered_map<std::string, py::object>{};
auto bind_enums(py::module mod) -> void
{
for (auto& [py_name, spec]: enums) {
auto const& [py_base_cls, pairs] =
spec.cast<std::pair<std::string, py::object>>();
mod.attr(py::cast(py_name)) = spec =
py::module::import("enum").attr(py_base_cls.c_str())(
py_name, pairs, py::arg("module") = mod.attr("__name__"));
}
}
}
}
// Immediately converting the args to a vector outside of the lambda avoids
// name collisions.
#define P11X_DECLARE_ENUM(py_name, py_base_cls, ...) \
namespace p11x { \
namespace { \
[[maybe_unused]] auto const P11X_CAT(enum_placeholder_, __COUNTER__) = \
[](auto args) { \
py::gil_scoped_acquire gil; \
using int_t = std::underlying_type_t<decltype(args[0].second)>; \
auto pairs = std::vector<std::pair<std::string, int_t>>{}; \
for (auto& [k, v]: args) { \
pairs.emplace_back(k, int_t(v)); \
} \
p11x::enums[py_name] = pybind11::cast(std::pair{py_base_cls, pairs}); \
return 0; \
} (std::vector{std::pair __VA_ARGS__}); \
} \
} \
namespace pybind11::detail { \
template<> struct type_caster<P11X_ENUM_TYPE(__VA_ARGS__)> { \
using type = P11X_ENUM_TYPE(__VA_ARGS__); \
static_assert(std::is_enum_v<type>, "Not an enum"); \
PYBIND11_TYPE_CASTER(type, _(py_name)); \
bool load(handle src, bool) { \
auto cls = p11x::enums.at(py_name); \
PyObject* tmp = nullptr; \
if (pybind11::isinstance(src, cls) \
&& (tmp = PyNumber_Index(src.attr("value").ptr()))) { \
auto ival = PyLong_AsLong(tmp); \
value = decltype(value)(ival); \
Py_DECREF(tmp); \
return !(ival == -1 && !PyErr_Occurred()); \
} else { \
return false; \
} \
} \
static handle cast(decltype(value) obj, return_value_policy, handle) { \
auto cls = p11x::enums.at(py_name); \
return cls(std::underlying_type_t<type>(obj)).inc_ref(); \
} \
}; \
}
#endif /* MPL_ENUMS_H */