Adjusting `type_caster<std::reference_wrapper<T>>` to support const/non-const propagation in `cast_op`. (#2705)
* Allow type_caster of std::reference_wrapper<T> to be the same as a native reference.
Before, both std::reference_wrapper<T> and std::reference_wrapper<const T> would
invoke cast_op<type>. This doesn't allow the type_caster<> specialization for T
to distinguish reference_wrapper types from value types.
After, the type_caster<> specialization invokes cast_op<type&>, which allows
reference_wrapper to behave in the same way as a native reference type.
* Add tests/examples for std::reference_wrapper<const T>
* Add tests which use mutable/immutable variants
This test is a chimera; it blends the pybind11 casters with a custom
pytype implementation that supports immutable and mutable calls.
In order to detect the immutable/mutable state, the cast_op needs
to propagate it, even through e.g. std::reference<const T>
Note: This is still a work in progress; some things are crashing,
which likely means that I have a refcounting bug or something else
missing.
* Add/finish tests that distinguish const& from &
Fixes the bugs in my custom python type implementation,
demonstrate test that requires const& and reference_wrapper<const T>
being treated differently from Non-const.
* Add passing a const to non-const method.
* Demonstrate non-const conversion of reference_wrapper in tests.
Apply formatting presubmit check.
* Fix build errors from presubmit checks.
* Try and fix a few more CI errors
* More CI fixes.
* More CI fixups.
* Try and get PyPy to work.
* Additional minor fixups. Getting close to CI green.
* More ci fixes?
* fix clang-tidy warnings from presubmit
* fix more clang-tidy warnings
* minor comment and consistency cleanups
* PyDECREF -> Py_DECREF
* copy/move constructors
* Resolve codereview comments
* more review comment fixes
* review comments: remove spurious &
* Make the test fail even when the static_assert is commented out.
This expands the test_freezable_type_caster a bit by:
1/ adding accessors .is_immutable and .addr to compare identity
from python.
2/ Changing the default cast_op of the type_caster<> specialization
to return a non-const value. In normal codepaths this is a reasonable
default.
3/ adding roundtrip variants to exercise the by reference, by pointer
and by reference_wrapper in all call paths. In conjunction with 2/, this
demonstrates the failure case of the existing std::reference_wrpper conversion,
which now loses const in a similar way that happens when using the default cast_op_type<>.
* apply presubmit formatting
* Revert inclusion of test_freezable_type_caster
There's some concern that this test is a bit unwieldly because of the use
of the raw <Python.h> functions. Removing for now.
* Add a test that validates const references propagation.
This test verifies that cast_op may be used to correctly detect
const reference types when used with std::reference_wrapper.
* mend
* Review comments based changes.
1. std::add_lvalue_reference<type> -> type&
2. Simplify the test a little more; we're never returning the ConstRefCaster
type so the class_ definition can be removed.
* formatted files again.
* Move const_ref_caster test to builtin_casters
* Review comments: use cast_op and adjust some comments.
* Simplify ConstRefCasted test
I like this version better as it moves the assertion that matters
back into python.
