I don't think that's right. It seems far-fetched that the compiler would know that accessing key_data->label() implies that k_d->has_value() == true I believe

I don't think that's right. It seems far-fetched that the compiler would know that accessing key_data->label() implies that k_d->has_value() == true I believe the explanation is: A && B : compiler will evaluate B only if A==true A & B : compiler will evaluate both A (safe) and B (unsafe), then perform bitwise operation