Request for "tagging" arguments with default without needing to duplicate the default values

Could pybind11 support default arguments for constructors without having to repeat the defaults, using something like this:

py::class_<Foo> c(m, "Foo");
c.def(py::init<
    const std::shared_ptr<bar>&,
    const std::array<double, 3>&,
    py::optional<
        const double,
        const double
    >
>());

this would be shortcut for:

py::class_<Foo> c(m, "Foo");

c.def(py::init<
    const std::shared_ptr<bar>&,
    const std::array<double, 3>&,
>());


c.def(py::init<
    const std::shared_ptr<bar>&,
    const std::array<double, 3>&,
    const double
>());

c.def(py::init<
    const std::shared_ptr<bar>&,
    const std::array<double, 3>&,
    const double,
    const double
>());

Note that Boost.Python supports this syntax.

Start by reading the proposed py::class_ and py::init syntax and compare it with the linked Boost.Python optional initializer documentation. Determine how the requested tagging form should expand to the shown constructor overloads without repeating defaults. Done means pybind11 supports the proposed default-argument syntax with equivalent constructor behavior.