ext: Updated Pybind11 to version 2.4.1.

This updates Pybind11 from version 2.2.1 to version 2.4.1. This fixes
warning/error received when "<experiment/optional>" is used when
compiling using c++14 with clang. It should be noted that
"ext/pybind11/include/pybind11/std.h" has been changed to include a fix
added by commit ba42457254cc362eddc099f22b60d469cc6369e0. This is
necessary to avoid build errors.

Built: Linux (gcc, c++11) and MacOS (clang, c++14).
Tested: Ran quick tests for X86, ARM, and RISC-V.
Deprecates: https://gem5-review.googlesource.com/c/public/gem5/+/21019
Change-Id: Ie9783511cb6be50136076a55330e645f4f36d075
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21119
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

1 files changed, 37 insertions, 5 deletions

diff --git a/ext/pybind11/docs/classes.rst b/ext/pybind11/docs/classes.rst
index ca2477e83..a63f6a196 100644
--- a/ext/pybind11/docs/classes.rst
+++ b/ext/pybind11/docs/classes.rst
@@ -155,6 +155,9 @@ the setter and getter functions:
             .def_property("name", &Pet::getName, &Pet::setName)
             // ... remainder ...
 
+Write only properties can be defined by passing ``nullptr`` as the
+input for the read function.
+
 .. seealso::
 
     Similar functions :func:`class_::def_readwrite_static`,
@@ -225,8 +228,8 @@ just brings them on par.
 
 .. _inheritance:
 
-Inheritance and automatic upcasting
-===================================
+Inheritance and automatic downcasting
+=====================================
 
 Suppose now that the example consists of two data structures with an
 inheritance relationship:
@@ -295,7 +298,7 @@ inheritance relationship. This is reflected in Python:
 
     >>> p = example.pet_store()
     >>> type(p)  # `Dog` instance behind `Pet` pointer
-    Pet          # no pointer upcasting for regular non-polymorphic types
+    Pet          # no pointer downcasting for regular non-polymorphic types
     >>> p.bark()
     AttributeError: 'Pet' object has no attribute 'bark'
 
@@ -327,11 +330,11 @@ will automatically recognize this:
 
     >>> p = example.pet_store2()
     >>> type(p)
-    PolymorphicDog  # automatically upcast
+    PolymorphicDog  # automatically downcast
     >>> p.bark()
     u'woof!'
 
-Given a pointer to a polymorphic base, pybind11 performs automatic upcasting
+Given a pointer to a polymorphic base, pybind11 performs automatic downcasting
 to the actual derived type. Note that this goes beyond the usual situation in
 C++: we don't just get access to the virtual functions of the base, we get the
 concrete derived type including functions and attributes that the base type may
@@ -419,6 +422,17 @@ on constness, the ``py::const_`` tag should be used:
        .def("foo_mutable", py::overload_cast<int, float>(&Widget::foo))
        .def("foo_const",   py::overload_cast<int, float>(&Widget::foo, py::const_));
 
+If you prefer the ``py::overload_cast`` syntax but have a C++11 compatible compiler only,
+you can use ``py::detail::overload_cast_impl`` with an additional set of parentheses:
+
+.. code-block:: cpp
+
+    template <typename... Args>
+    using overload_cast_ = pybind11::detail::overload_cast_impl<Args...>;
+
+    py::class_<Pet>(m, "Pet")
+        .def("set", overload_cast_<int>()(&Pet::set), "Set the pet's age")
+        .def("set", overload_cast_<const std::string &>()(&Pet::set), "Set the pet's name");
 
 .. [#cpp14] A compiler which supports the ``-std=c++14`` flag
             or Visual Studio 2015 Update 2 and newer.
@@ -485,6 +499,24 @@ The entries defined by the enumeration type are exposed in the ``__members__`` p
     >>> Pet.Kind.__members__
     {'Dog': Kind.Dog, 'Cat': Kind.Cat}
 
+The ``name`` property returns the name of the enum value as a unicode string.
+
+.. note::
+
+    It is also possible to use ``str(enum)``, however these accomplish different
+    goals. The following shows how these two approaches differ.
+
+    .. code-block:: pycon
+
+        >>> p = Pet( "Lucy", Pet.Cat )
+        >>> pet_type = p.type
+        >>> pet_type
+        Pet.Cat
+        >>> str(pet_type)
+        'Pet.Cat'
+        >>> pet_type.name
+        'Cat'
+
 .. note::
 
     When the special tag ``py::arithmetic()`` is specified to the ``enum_``