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He discovered member initialization lists (a basic C++ feature, covered on page 3 in most C++ books).

Actually, what I discovered was that member initialization could be used with references. This was not obvious to me when I read the first edition of Stroustrup years ago. The current edition does mention it.

And having a reference does not guarantee that the underlying object is still alive.
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No, it doesn't. Which is why you would only want to do this with objects that have to stick around for the referring object to work at all.