HepMC3 event record library
functional.h
1 /*
2  pybind11/functional.h: std::function<> support
3 
4  Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
5 
6  All rights reserved. Use of this source code is governed by a
7  BSD-style license that can be found in the LICENSE file.
8 */
9 
10 #pragma once
11 
12 #include "pybind11.h"
13 #include <functional>
14 
15 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
16 PYBIND11_NAMESPACE_BEGIN(detail)
17 
18 template <typename Return, typename... Args>
19 struct type_caster<std::function<Return(Args...)>> {
20  using type = std::function<Return(Args...)>;
21  using retval_type = conditional_t<std::is_same<Return, void>::value, void_type, Return>;
22  using function_type = Return (*) (Args...);
23 
24 public:
25  bool load(handle src, bool convert) {
26  if (src.is_none()) {
27  // Defer accepting None to other overloads (if we aren't in convert mode):
28  if (!convert) return false;
29  return true;
30  }
31 
32  if (!isinstance<function>(src))
33  return false;
34 
35  auto func = reinterpret_borrow<function>(src);
36 
37  /*
38  When passing a C++ function as an argument to another C++
39  function via Python, every function call would normally involve
40  a full C++ -> Python -> C++ roundtrip, which can be prohibitive.
41  Here, we try to at least detect the case where the function is
42  stateless (i.e. function pointer or lambda function without
43  captured variables), in which case the roundtrip can be avoided.
44  */
45  if (auto cfunc = func.cpp_function()) {
46  auto c = reinterpret_borrow<capsule>(PyCFunction_GET_SELF(cfunc.ptr()));
47  auto rec = (function_record *) c;
48 
49  if (rec && rec->is_stateless &&
50  same_type(typeid(function_type), *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
51  struct capture { function_type f; };
52  value = ((capture *) &rec->data)->f;
53  return true;
54  }
55  }
56 
57  // ensure GIL is held during functor destruction
58  struct func_handle {
59  function f;
60  func_handle(function&& f_) : f(std::move(f_)) {}
61  func_handle(const func_handle& f_) {
63  f = f_.f;
64  }
65  ~func_handle() {
67  function kill_f(std::move(f));
68  }
69  };
70 
71  // to emulate 'move initialization capture' in C++11
72  struct func_wrapper {
73  func_handle hfunc;
74  func_wrapper(func_handle&& hf): hfunc(std::move(hf)) {}
75  Return operator()(Args... args) const {
77  object retval(hfunc.f(std::forward<Args>(args)...));
78  /* Visual studio 2015 parser issue: need parentheses around this expression */
79  return (retval.template cast<Return>());
80  }
81  };
82 
83  value = func_wrapper(func_handle(std::move(func)));
84  return true;
85  }
86 
87  template <typename Func>
88  static handle cast(Func &&f_, return_value_policy policy, handle /* parent */) {
89  if (!f_)
90  return none().inc_ref();
91 
92  auto result = f_.template target<function_type>();
93  if (result)
94  return cpp_function(*result, policy).release();
95  else
96  return cpp_function(std::forward<Func>(f_), policy).release();
97  }
98 
99  PYBIND11_TYPE_CASTER(type, _("Callable[[") + concat(make_caster<Args>::name...) + _("], ")
100  + make_caster<retval_type>::name + _("]"));
101 };
102 
103 PYBIND11_NAMESPACE_END(detail)
104 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)
function_record
Internal data structure which holds metadata about a bound function (signature, overloads,...
Definition: attr.h:141
type
Definition: pytypes.h:904
object::release
handle release()
Definition: pytypes.h:249
handle::inc_ref
const handle & inc_ref() const &
Definition: pytypes.h:192
handle
Definition: pytypes.h:176
type_caster
Definition: cast.h:946
cpp_function
Wraps an arbitrary C++ function/method/lambda function/.. into a callable Python object.
Definition: pybind11.h:62
gil_scoped_acquire
Definition: pybind11.h:2176
void_type
Helper type to replace 'void' in some expressions.
Definition: detail/common.h:560
args
Definition: pytypes.h:1341
function
Definition: pytypes.h:1361
none
Definition: pytypes.h:1064