This commit introduces the use of C++17-style fold expressions when
casting tuples & the argument lists of functions.
This change can improve performance of the resulting bindings: because
fold expressions have short-circuiting semantics, pybind11 e.g. won't
try to cast the second argument of a function if the first one failed.
This is particularly effective when working with functions that have
many overloads with long argument lists.
* test pair-copyability on C++17 upwards
The stdlib falsely detects containers like M=std::map<T, U>
as copyable, even when one of T and U is not copyable.
Therefore we cannot rely on the stdlib dismissing std::pair<T, M>
by itself, even on C++17.
* fix is_copy_assignable
bind_map used std::is_copy_assignable which suffers from the same problems
as std::is_copy_constructible, therefore the same fix has been applied.
* created tests for copyability
Don't assume that just because the language version is C++17 that the
standard library offers all C++17 features, too. When using clang-6.0
and --std=c++17 on Ubuntu 18.04 with libstdc++, __cpp_sized_deallocation
is false.
When building with `-Werror,-Wmissing-prototypes`, `clang` complains about missing prototypes for functions defined through macro expansions. This PR adds the missing prototypes.
```
error: no previous prototype for function 'pybind11_init_impl_embedded' [
-Werror,-Wmissing-prototypes]
PYBIND11_EMBEDDED_MODULE(embedded, mod) {
^
external/pybind11/include/pybind11/embed.h:61:5: note: expanded from macro 'PYBIND11_EMBEDDED_MODULE'
PYBIND11_EMBEDDED_MODULE_IMPL(name) \
^
external/pybind11/include/pybind11/embed.h:26:23: note: expanded from macro 'PYBIND11_EMBEDDED_MODULE_IMPL'
extern "C" void pybind11_init_impl_##name() { \
^
<scratch space>:380:1: note: expanded from here
pybind11_init_impl_embedded
^
1 error generated.
```
* Adapt to python3.8 C API change
Do `Py_DECREF(type)` on all python objects on deallocation
fix#1946
* Add bare python3.8 build to CI matrix
While numpy/scipy wheels are available, run python3.8 test without them
* fix: Avoid conversion to `int_` rhs argument of enum eq/ne
* test: compare unscoped enum with strings
* suppress comparison to None warning
* test unscoped enum arithmetic and comparision with unsupported type
