C++: Is initializing a static local variable with a IIFE thread-safe?

Question

Is the following code thread-safe? (Using a IIFE to initialize a static local variable.)

int MyFunc(){

static int Val = ([]()
   {
   return 1 + 2 + 3 + 4; // Real code is more complex, but thread-safe
   })();

return Val;

}

Answer 1

Yes. C++11 (and above) guarantees no data races between multiple threads trying to initialize a static local variable. If the code inside your lambda is thread-safe, the initialization will be as well.

Using a lambda, function call, or constructor doesn't change the thread-safety of the initialization.