Rule 3-4-1 and lifetimes, initialization, and side effects

[aromauld]

We have some interesting cases for Rule 3-4-1 which we aren't sure whether they are violations or not. Strictly adhering to the rule of reduced visibility could cause issues regarding lifetimes, initialization, and side effects of a constructor/destructor.

For instance, in the following example, is the intent to require changes to the code so that 'old_value' is not visible after the if body, or is `old_value` considered non-violating?

Code:

void fn(int a) {
    int old_value = a;
    a += 4;
    if (a > 10) {
        a = old_value;
    }
    // ...
}

Similarly, in cases where an object's constructor or destructor contains side effects, such as with a mutex, is the current visibility of 'merge_thread_lock' intended to be a violation?

Code:

void fn(int a) {
    std::unique_lock<std::shared_mutex> merge_thread_lock(global_mutex);
    if (global) {
      global = a;
      merge_thread_lock.unlock();
    }
    // ...
}