When a C++ lambda expression has a lot of captures by reference, the size of the unnamed function object becomes large

Question

The following code:

int main() {
    int a, b, c, d, e, f, g;
    auto func = [&](){cout << a << b << c << d << e <<          


        

Answer 1

I do not understand why you seem surprised.

The C++ Standard gives a set of requirements, and every single implementation is free to pick any strategy that meets the requirements.

Why would an implementation optimize the size of the lambda object ?

Specifically, do you realize how that would tie down the generated code of this lambda to the generated code for the surrounding function ?

It's easy to say Hey! This could be optimized!, but it's much more difficult to actually optimize and make sure it works in all edge cases. So, personally, I much prefer having a simple and working implementation than a botched attempt at optimizing it...

... especially when the work-around is so easy:

struct S { int a, b, c, d, e, f, g; };

int main() {
    S s = {};
    auto func = [&](){
        std::cout << s.a << s.b << s.c << s.d << s.e << s.f << s.g << "\n";
    };
    std::cout << sizeof(func) << "\n";
    return 0;
}

Look Ma: 4 bytes only!