1.. title:: clang-tidy - cppcoreguidelines-misleading-capture-default-by-value
2
3cppcoreguidelines-misleading-capture-default-by-value
4=====================================================
5
6Warns when lambda specify a by-value capture default and capture ``this``.
7
8By-value capture defaults in member functions can be misleading about whether
9data members are captured by value or reference. This occurs because specifying
10the capture default ``[=]`` actually captures the ``this`` pointer by value,
11not the data members themselves. As a result, data members are still indirectly
12accessed via the captured ``this`` pointer, which essentially means they are
13being accessed by reference. Therefore, even when using ``[=]``, data members
14are effectively captured by reference, which might not align with the user's
15expectations.
16
17Examples:
18
19.. code-block:: c++
20
21      struct AClass {
22        int member;
23        void misleadingLogic() {
24          int local = 0;
25          member = 0;
26          auto f = [=]() mutable {
27            local += 1;
28            member += 1;
29          };
30          f();
31          // Here, local is 0 but member is 1
32        }
33
34        void clearLogic() {
35          int local = 0;
36          member = 0;
37          auto f = [this, local]() mutable {
38            local += 1;
39            member += 1;
40          };
41          f();
42          // Here, local is 0 but member is 1
43        }
44      };
45
46This check implements `F.54
47<https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#f54-when-writing-a-lambda-that-captures-this-or-any-class-data-member-dont-use--default-capture>`_
48from the C++ Core Guidelines.
49