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