Is a back_insert_iterator valid for the lifetime of the container?

I think I know the answer to this, but I'd appreciate a sanity check.


Does iterator invalidation apply to std::back_insert_iterators?
#include
#include
#include

int main() {
auto v = std::vector{ 0, 1, 2 };
auto iter = std::back_inserter(v);
*iter++ = 3;
v.clear(); // invalidates iterators, but
*iter++ = 4; // back_insert_iterator is special?
assert(v.size() == 1 && v[0] == 4);
return 0;
}



This code works for me because the std::back_insert_iterator implementation from my vendor doesn't hold an iterator (or pointer or reference). It simply calls the container's push_back method.


But does the standard require that implementation? Could another vendor's back_insert_iterator hold and maintain a one-past-the-end iterator to use with a call to the container's insert method? It seems that would meet the requirements. This difference, of course, is that it would be vulnerable to invalidation.

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I know cppreference.com is not authoritative, but it's more accessible than the standard.



[A vector's clear method] [i]nvalidates any ... iterators referring to contained elements. Any past-the-end iterators are also invalidated. [cppreference.com, emphasis added]



A std::back_insert_iterator could be the poster child of a past-the-end iterator.