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:

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 from the C++ Core Guidelines.