forked from OSchip/llvm-project
42 lines
1.9 KiB
ReStructuredText
42 lines
1.9 KiB
ReStructuredText
.. title:: clang-tidy - modernize-replace-random-shuffle
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modernize-replace-random-shuffle
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================================
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This check will find occurrences of ``std::random_shuffle`` and replace it with ``std::shuffle``. In C++17 ``std::random_shuffle`` will no longer be available and thus we need to replace it.
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Below are two examples of what kind of occurrences will be found and two examples of what it will be replaced with.
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.. code-block:: c++
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std::vector<int> v;
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// First example
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std::random_shuffle(vec.begin(), vec.end());
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// Second example
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std::random_shuffle(vec.begin(), vec.end(), randomFunc);
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Both of these examples will be replaced with:
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.. code-block:: c++
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std::shuffle(vec.begin(), vec.end(), std::mt19937(std::random_device()()));
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The second example will also receive a warning that ``randomFunc`` is no longer supported in the same way as before so if the user wants the same functionality, the user will need to change the implementation of the ``randomFunc``.
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One thing to be aware of here is that ``std::random_device`` is quite expensive to initialize. So if you are using the code in a performance critical place, you probably want to initialize it elsewhere.
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Another thing is that the seeding quality of the suggested fix is quite poor: ``std::mt19937`` has an internal state of 624 32-bit integers, but is only seeded with a single integer. So if you require
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higher quality randomness, you should consider seeding better, for example:
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.. code-block:: c++
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std::shuffle(v.begin(), v.end(), []() {
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std::mt19937::result_type seeds[std::mt19937::state_size];
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std::random_device device;
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std::uniform_int_distribution<typename std::mt19937::result_type> dist;
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std::generate(std::begin(seeds), std::end(seeds), [&] { return dist(device); });
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std::seed_seq seq(std::begin(seeds), std::end(seeds));
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return std::mt19937(seq);
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}());
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