It was certainly how I learned to do it, but lambdas have been around for over a decade and I still see people writing functors. The only use case I've seen where it made sense is for things like coroutines.
For std::visit() (std::variant.visit in c++26 I see) which is the visitor pattern, you can use a functor with multiple visit types or roll your own overload() template to merge multiple lambdas into one class.
But why would I want to do this instead of just having multiple lambdas that capture the same values by reference, or using shared_ptr and synchronization? I can see lifetimes of the data being an issue, but you shouldn't be calling std::visit in a way where that could cause a problem without synchronization anyway.
Lambdas these days cover 99% of the needs for custom function objects. But for that 1% it is useful to be able to have full control of your closure.
For example how would you implement std::function without overloaded operator()?
Also lambdas are defined in term of structs with overloaded operator ().
Without overloading, the standard could still ad-hoc define the specifications of lambdas and std::function, std:: ref, etc, but the language would be worse off.
That example seems contrived. Why would I want to know something was called n-times? Even for benchmarking I would just capture an integer and increment it.
To be mildly pedantic, printing in a destructor is horrible practice because stdout/stderr might be pipes or sockets and writing might fail. It's a really bad idea to do anything in a destructor that effects anything but the class being destroyed for those reasons, and when you get an error, it shows up as an opaque exception or trace or hang at the end of a scope instead of where it actually mattered.
I actually ran into that at work a few days ago. I wanted to provide a callback that accumulated stuff, and check that the total was equal to what was expected, or crash the program otherwise (fail fast). I could have equivalently written the output of the test to a capture-by-ref variable and checked it outside if I really wanted to.
