I have seen many answers on SO asking about capturing this by reference but I have a different question. What if I want to capture a specific variable owned by this object?
For example:
auto rel_pose = [this->_last_pose["main_pose"],&pose](Eigen::VectorXd pose1, Eigen::VectorXd pose2)
{
// Some code
return pose;
};
I want to capture the specific variable of this by value and use it inside my lambda expression. Why this is not possible?
You can apply by-copy capture with an initializer (since C++14) (or by-reference capture with an initializer, depends on your demand), e.g.
auto rel_pose = [some_pose = this->_last_pose["main_pose"], &pose](Eigen::VectorXd pose1, Eigen::VectorXd pose2)
{
// Some code using some_pose
return pose;
};
Note that we can only capture identifiers in lambda, we can't capture expressions like this->_last_pose["main_pose"] directly. The captures with an initializer just solve such issues straightforward.
It's possible:
struct S
{
int i = 7;
char c = 0;
};
int main(int argc, char* argv[])
{
S s;
auto l = [integer = s.i]() {
return integer;
};
return l();
}
Why this is not possible?
It's possible, like other answers show. But you must do it explicitly. Accessing any member of the current object in the lambda is transformed automatically to an access through the this pointer. When you write a plain [this->_last_pose["main_pose"],&pose], what's really captured is this, and the access to _last_pose goes through it.
It's simply how lambda captures are specified for member variables. Be grateful you are compiling C++14. In C++11 capturing members by value was not as easy as adding an init capture that does an copy.
