88 lines
2.4 KiB
ReStructuredText
88 lines
2.4 KiB
ReStructuredText
.. title:: clang-tidy - modernize-avoid-bind
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modernize-avoid-bind
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====================
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The check finds uses of ``std::bind`` and ``boost::bind`` and replaces them
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with lambdas. Lambdas will use value-capture unless reference capture is
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explicitly requested with ``std::ref`` or ``boost::ref``.
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It supports arbitrary callables including member functions, function objects,
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and free functions, and all variations thereof. Anything that you can pass
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to the first argument of ``bind`` should be diagnosable. Currently, the only
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known case where a fix-it is unsupported is when the same placeholder is
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specified multiple times in the parameter list.
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Given:
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.. code-block:: c++
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int add(int x, int y) { return x + y; }
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Then:
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.. code-block:: c++
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void f() {
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int x = 2;
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auto clj = std::bind(add, x, _1);
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}
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is replaced by:
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.. code-block:: c++
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void f() {
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int x = 2;
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auto clj = [=](auto && arg1) { return add(x, arg1); };
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}
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``std::bind`` can be hard to read and can result in larger object files and
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binaries due to type information that will not be produced by equivalent
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lambdas.
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Options
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-------
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.. option:: PermissiveParameterList
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If the option is set to `true`, the check will append ``auto&&...`` to the end
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of every placeholder parameter list. Without this, it is possible for a fix-it
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to perform an incorrect transformation in the case where the result of the ``bind``
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is used in the context of a type erased functor such as ``std::function`` which
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allows mismatched arguments. For example:
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.. code-block:: c++
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int add(int x, int y) { return x + y; }
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int foo() {
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std::function<int(int,int)> ignore_args = std::bind(add, 2, 2);
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return ignore_args(3, 3);
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}
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is valid code, and returns `4`. The actual values passed to ``ignore_args`` are
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simply ignored. Without ``PermissiveParameterList``, this would be transformed into
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.. code-block:: c++
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int add(int x, int y) { return x + y; }
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int foo() {
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std::function<int(int,int)> ignore_args = [] { return add(2, 2); }
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return ignore_args(3, 3);
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}
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which will *not* compile, since the lambda does not contain an ``operator()``
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that accepts 2 arguments. With permissive parameter list, it instead generates
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.. code-block:: c++
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int add(int x, int y) { return x + y; }
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int foo() {
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std::function<int(int,int)> ignore_args = [](auto&&...) { return add(2, 2); }
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return ignore_args(3, 3);
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}
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which is correct.
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This check requires using C++14 or higher to run.
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