How to stop lambda modifying class member

Question

Refer code below :

I have a method of class which uses lambda and modifies member variable from lambda.

This lambda has = as capture clause. I thought a should not be modified, but it allows modification. Do we have any mechanism which stops this modification?
https://sololearn.com/compiler-playground/cqry108RT02o/?ref=app

Answer 1

You can add access specifiers.
Also, a struct is meant for variables. How about you extract the methods out of it and put it in a class?