Non-const lambda capture in const method - c++

Question

#include <iostream>
#include <functional>
class Blub {
public:
int i = 0;
std::function<void()> create() const {
return [this]() {
this->i = 100;
};
}
};
int main() {
Blub blub = Blub();
blub.create()();
std::cout << blub.i << std::endl;
return 0;
}
I know that this is captured as const inside the lambda, because the method is marked const.
Is there still a way, aside from removing the constness of the method, to archive that i can modify member variables inside the lambda function?
Adding mutable keyword is not working.

Answer 1

You can declare the member variable i as mutable, so that it could change even if the object is declared as const:
class Blub {
public:
mutable int i = 0;
// ^^^^^^^
std::function<void()> create() const {
return [this]() {
this->i = 100;
};
}
};
Live here.

Answer 2

You can do the following workaround:
class Blub {
public:
int i = 0;
std::function<void()> create() const {
return [my_this=const_cast<Blub*>(this)]() {
my_this->i = 100;
};
}
};
but it is misleading to change a data member in a function which is actually marked as const so I wouldn't suggest designing your class in that way.
Check it out live.
N.B. It is worth to mention that const_cast is safe to use only if it's used for casting a variable that was originally non-const. If the variable is originally const, using const_cast could result in Undefined Behavior. So, in the following code (which the OP provided):
int main() {
Blub blub = Blub();
blub.create()();
std::cout << blub.i << std::endl;
return 0;
}
it is safe to use const_cast because object is originally made non-const. However, if we make it const like in the following code:
int main() {
const Blub blub = Blub();
blub.create()();
std::cout << blub.i << std::endl;
return 0;
}
it will result in an Undefined Behavior.