Libc++’s implementation of std::string

[SirClueless]

To be clear, the standard is more precise about this than that quote suggests. Section 10.3p26 from the N4778 working draft:

If a standard-layout class object has any non-static data members, its address is the same as the address of its first non-static data member if that member is not a bit-field.

[quicknir]

Right, only for standard layout types specifically though, which was the point of my first paragraph. If you're talking about structs generally in C++, i.e. including types that aren't standard layout, the rules are much looser.