c++ - Are there any undefined behavior issues when moving data into a function and then back out to where it came from? -

consider following function:

std::vector<int> pushit(std::vector<int> v){     v.push_back(10);     return v;  }  int main(){     std::vector<int> vec;     vec = pushit(std::move(vec)); } 

my assumption vector moved function, modified , moved original spot. should result in simmilar behavior passing in non const reference. seems quite valid behavior colleague fears undefined behavior. there missing here?

i because current function

void currentpushit(std::vector<int>& v){     v.push_back(10); } 

has led lot of problems in code review because people overlook fact innocent call currentpushit(v) can invalidate iterators. making them write v=pushit(std::move(v)) should wake them enough don't make same mistakes.

per 1.9p15, value computations , side effects associated argument sequenced before execution of body of function. time enter pushit source vec has been moved from. assignment sequenced after execution of pushit, since calling user-defined operator vector::operator=:

vec.operator=(       // sequenced after     pushit(          // evaluation of this, sequenced after         std::move(   // evaluation of             vec))) 

so code fine.