1*6e566bc5SRichard.. title:: clang-tidy - portability-std-allocator-const 2*6e566bc5SRichard 3*6e566bc5SRichardportability-std-allocator-const 4*6e566bc5SRichard=============================== 5*6e566bc5SRichard 6*6e566bc5SRichardReport use of ``std::vector<const T>`` (and similar containers of const 7*6e566bc5SRichardelements). These are not allowed in standard C++, and should usually be 8*6e566bc5SRichard``std::vector<T>`` instead." 9*6e566bc5SRichard 10*6e566bc5SRichardPer C++ ``[allocator.requirements.general]``: "T is any cv-unqualified object 11*6e566bc5SRichardtype", ``std::allocator<const T>`` is undefined. Many standard containers use 12*6e566bc5SRichard``std::allocator`` by default and therefore their ``const T`` instantiations are 13*6e566bc5SRichardundefined. 14*6e566bc5SRichard 15*6e566bc5SRichardlibc++ defines ``std::allocator<const T>`` as an extension which will be removed 16*6e566bc5SRichardin the future. 17*6e566bc5SRichard 18*6e566bc5SRichardlibstdc++ and MSVC do not support ``std::allocator<const T>``: 19*6e566bc5SRichard 20*6e566bc5SRichard.. code:: c++ 21*6e566bc5SRichard 22*6e566bc5SRichard // libstdc++ has a better diagnostic since https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48101 23*6e566bc5SRichard std::deque<const int> deque; // error: static assertion failed: std::deque must have a non-const, non-volatile value_type 24*6e566bc5SRichard std::set<const int> set; // error: static assertion failed: std::set must have a non-const, non-volatile value_type 25*6e566bc5SRichard std::vector<int* const> vector; // error: static assertion failed: std::vector must have a non-const, non-volatile value_type 26*6e566bc5SRichard 27*6e566bc5SRichard // MSVC 28*6e566bc5SRichard // error C2338: static_assert failed: 'The C++ Standard forbids containers of const elements because allocator<const T> is ill-formed.' 29*6e566bc5SRichard 30*6e566bc5SRichardCode bases only compiled with libc++ may accrue such undefined usage. This 31*6e566bc5SRichardcheck finds such code and prevents backsliding while clean-up is ongoing. 32