如何静态转换指向常量成员函数的指针

Question

令人惊讶(尴尬？(的是，我无法正确理解const成员函数的static_const的语法。简而言之(详细信息如下(，如果成员函数没有标记为const，我使用：

static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&)>(&mymodule::Foo::bar)

但在标记成员函数Foo::bar(...) const时，编译器不知道该做什么：

error: address of overloaded function 'bar' cannot be static_cast to type 'std::vector<double> (mymodule::Foo::*)(const std::vector<double> &)'

我应该把函数的const放在哪里？

详细信息

我正在尝试为以下模块创建Python绑定：

namespace mymodule {
class Foo
{
public:
Foo() = default;
template <class T>
T bar(const T& a) const
{
T ret = a;
for (auto& i : ret) {
i *= 2.0;
}
return ret;
}
template <class T>
T bar(const T& a, double f) const
{
T ret = a;
for (auto& i : ret) {
i *= f;
}
return ret;
}
};
} // namespace mymodule

我用pybind11:编写Python绑定

#include <pybind11/pybind11.h>
namespace py = pybind11;
PYBIND11_MODULE(example, m)
{
py::class_<mymodule::Foo>(m, "Foo")
.def(py::init<>())
.def("bar",
static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&)>(&mymodule::Foo::bar),
py::arg("a"))
.def("bar",
static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&, double)>(&mymodule::Foo::bar),
py::arg("a"),
py::arg("f"));
}

编译失败：

.../example.cpp:54:14: error: address of overloaded function 'bar' cannot be static_cast to type 'std::vector<double> (mymodule::Foo::*)(const std::vector<double> &)'
static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&)>(&mymodule::Foo::bar),
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../example.cpp:19:7: note: candidate function template
T bar(const T& a) const
^
.../example.cpp:29:7: note: candidate function template
T bar(const T& a, double f) const
^
.../example.cpp:58:14: error: address of overloaded function 'bar' cannot be static_cast to type 'std::vector<double> (mymodule::Foo::*)(const std::vector<double> &, double)'
static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&, double)>(&mymodule::Foo::bar),
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../example.cpp:19:7: note: candidate function template
T bar(const T& a) const
^
.../example.cpp:29:7: note: candidate function template
T bar(const T& a, double f) const
^
2 errors generated.

Answer 1

您应该最后将const添加为：

static_cast<std::vector<double> (mymodule::Foo::*)(const std::vector<double>&) const>(&mymodule::Foo::bar),
//                                                                             ^^^^^