Table 68 in 23.1.1/12 specifies operational semantics for "a.back()"
as "*--a.end()", which may be ill-formed, provided a.end() returns a
simple pointer rvalue (this is almost always the case for
std::vector::end(), for example).
Thus, the specification is not only incorrect, it demonstrates a
dangerous construct: "--a.end()" may successfully compile and run as
intended, but after changing the type of the container or the mode of
compilation it may produce compile-time error.

I suggest changing the specification for "a.back()" from

"*--a.end()"

to

"{ X::iterator tmp = a.end(); return *--tmp; }"

and the specification for "a.pop_back()" from

"a.erase(--a.end())"

to

"{ X::iterator tmp = a.end(); a.erase(--tmp); }".

Yaroslav


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