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.. title:: clang-tidy - cppcoreguidelines-misleading-capture-default-by-value
cppcoreguidelines-misleading-capture-default-by-value
=====================================================
Warns when lambda specify a by-value capture default and capture ``this``.
By-value capture defaults in member functions can be misleading about whether
data members are captured by value or reference. This occurs because specifying
the capture default ``[=]`` actually captures the ``this`` pointer by value,
not the data members themselves. As a result, data members are still indirectly
accessed via the captured ``this`` pointer, which essentially means they are
being accessed by reference. Therefore, even when using ``[=]``, data members
are effectively captured by reference, which might not align with the user's
expectations.
Examples:
.. code-block:: c++
struct AClass {
int member;
void misleadingLogic() {
int local = 0;
member = 0;
auto f = [=]() mutable {
local += 1;
member += 1;
};
f();
// Here, local is 0 but member is 1
}
void clearLogic() {
int local = 0;
member = 0;
auto f = [this, local]() mutable {
local += 1;
member += 1;
};
f();
// Here, local is 0 but member is 1
}
};
This check implements `F.54
<https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#f54-when-writing-a-lambda-that-captures-this-or-any-class-data-member-dont-use--default-capture>`_
from the C++ Core Guidelines.
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