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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"PyUnicode_READ() fails to build on C++: _Py_CAST() used with a constant type (const void*)","articleBody":"**Bug report**\r\n\r\nThe new `_Py_CAST` macro (https://github.com/python/cpython/pull/91959/files, and other commits) designed to reduce C++ warnings adds a fairly significant restriction that wasn't there before\r\n\r\nhttps://github.com/python/cpython/blob/9f68dab3d327335b938046c50b4f09944e993cc8/Include/pyport.h#L25-L26\r\n\r\nThe PyUnicode_READ macro casts to a const pointer\r\n\r\nhttps://github.com/python/cpython/blob/9f68dab3d327335b938046c50b4f09944e993cc8/Include/cpython/unicodeobject.h#L341-L343\r\n\r\nThis is currently reported to be breaking Cython (https://github.com/cython/cython/issues/4790).\r\n\r\nI'd propose a fix which removes the const requirement:\r\n\r\n```\r\ntemplate \u003ctypename T\u003e\r\nstruct _Py_add_const {\r\n    typedef const T type;\r\n};\r\n#  define _Py_CAST(tp, expr) \\\r\n       const_cast\u003ctp\u003e(reinterpret_cast\u003c_Py_add_const\u003ctp\u003e::type\u003e(expr))\r\n```\r\n\r\non C++11 you could use the standard library `std::add_cast` instead, at the cost of an extra include. However it isn't available on c++03.\r\n\r\nI realise this adds an extra struct `_Py_add_const` to the namespace. I'm not sure if that's desired, or how it should be named. If that's acceptable I'm happy to submit a PR for this.\r\n\r\n@vstinner \r\n\r\n**Your environment**\r\n\r\nCurrent 3.11 branch\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n","author":{"url":"https://github.com/da-woods","@type":"Person","name":"da-woods"},"datePublished":"2022-05-14T08:00:05.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/92800/cpython/issues/92800"}