gh-92135: Fix _Py_reinterpret_cast() for const#92138
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MemberAuthor
vstinner commented May 2, 2022
@tacaswell@serge-sans-paille: Does my |
MemberAuthor
vstinner commented May 2, 2022
Contributor
erlend-aasland commented May 2, 2022
FTR, in another project, I recently had to use two casts in order to avoid G++ warnings: voidinner_set(void *); // original code (generated warnings)voidset_func(constchar *str){inner_set(str)} // new set func, still generated warningsvoidimproved_set_func(constchar *str){inner_set(const_cast<void *>(str))} // final set func, no warningsvoidset_func_without_warning(constchar *str){constvoid *vptr = static_cast<constvoid *>(str); inner_set(const_cast<void *>(vptr))} |
Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when casting a constant expression to a non constant type: use const_cast<> in C++. * In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than reinterpret_cast<>. * Add tests to the _testcppext C++ extension. * test_cppext no longer captures stdout in verbose mode.
vstinner changed the title MemberAuthor
vstinner commented May 2, 2022
I understand that this approach (updated First, I renamed the macro _Py_reinterpret_const_cast(), but @serge-sans-paille didn't like this name, and me neither (it's too long!). So I kept the name |
erlend-aasland approved these changes May 2, 2022
MemberAuthor
vstinner commented May 2, 2022
@tacaswell: This issue should now be fixed. Please try greenlet with on the main branch of Python. |
Contributor
tacaswell commented May 2, 2022
The const issues is fixed the other casting issues still remains |
MemberAuthor
vstinner commented May 3, 2022
I have no idea how to fix this cast. Do you have an idea? Does Maybe greenlet should be modified to cast to |
Contributor
tacaswell commented May 3, 2022
I think we need an actual C++ expert to tell us if what greenlets is doing is fully kosher or undefined behavior that just happened to work before.
python-greenlet/greenlet@50f8786 is one way that works. |
Contributor
serge-sans-paille commented May 4, 2022
That's an interesting situation: greenlets are written in C++, and the object that raises issues is of type According to me, this means we need something along these lines: |
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Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when
casting a constant expression to a non constant type: use
const_cast<> in C++.
reinterpret_cast<>.