This link is exactly what I'm saying, if you don't ask for it you don't get initialization. There are multiple ways to ask for it because the person who writes

This link is exactly what I'm saying, if you don't ask for it you don't get initialization. There are multiple ways to ask for it because the person who writes the type may eitherwant to take on the responsibility of initializing entirely by initializing on the ctor, or delegate it to the call site which can then either initialise (T t{};) or not (T t;). The SO post looks confused ; A, B, D, E and F are the exact same case wrt the initialization of the int. It does not matter that there's a constructor or not and which shape it has, only that the variables get initialization somewhere or not (and that can be in the ctor's member init list, in the struct définition or even when creating a value if aggregate-initializing).