some attributes in c++17

[[fallthrough]]

When we use [[fallthrough]] within the switch statement, we tell compiler that we intended to fall through from one case to another.

void do something(){}

void do_something_else(){}

int main(int argc, const char*[])
{
    switch(argc)
    {
        case 1:
            do_something;
            [[fallthrough]];
        case 2:
            do_something_else;
    }
}

[[maybe_unused]]

Usful for situation when compiler is going to warn you that something has unused that was defined.

#include <cassert>

[[maybe_unused]] void something()

int main(int /*argc*/, [[maybe_unused]] const char *argv[])
{
  [[maybe_unused]] int i=6;
  assert(i == 6);
}

[[no_discard]]

Tells compiler that return value of the function is important and should not be discarded.

[[nodiscard]]int something()
{
  return 1;
}

int main()
{
  return something;
}

[[nodiscard]] could also be applied to struct, enum, class, union, etc.

struct [[nodiscard]] MyError
{  
};

enum [[nodiscard]] MyError
{
  VAL1,
  VAL2
};

when trying to avoid exception while getting some level of guarentee that we are appropriately handling error code.