[Development] QVector now has rvalue push_back (was: Re: HEADS UP: potential trouble from a recent QVector change)

Bubke Marco Marco.Bubke at theqtcompany.com
Tue Jul 21 20:11:33 CEST 2015


Gunnar Roth <gunnar.roth at gmx.de>
> >
> >      void push_back(T &&t) {
> >          ensureCapacity(size() + 1);
> >          new (m_end) T(std::move(t));                // move-construct from t
> >          ++m_end;
> why is std::move needed here? Afaik std::move(t) converts t into a rvalue ref, but t is already an r-value ref.

If T would be not a template t is binding to a rvalue reference but it is not itself a rvalue reference but an lvalue.
If T is a template like in this case it is more complicated because it is a universal or forward reference. For a 
forward reference it could be an lvalue reference like (T&) or a lvalue(T) depending as the argument is a rvalue,
lvalue or lvalue reference. 
T&& -> T
T& -> T&
T -> T

std::forward would be of better use than std::move: 
http://en.cppreference.com/w/cpp/utility/forward




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