recently I've been reading through Scott Meyers's excellent Effective C++ book. In one of the last tips he covered some of the features from TR1 - I knew many of them via Boost.
However, there was one that I definitely did NOT recognize: tr1::reference_wrapper.
How and when would I use tr1::reference_wrapper?
It's like boost::ref, as far as I know. Basically, a reference which can be copied. Very useful when binding to functions where you need to pass parameters by reference.
For example (using boost syntax):
void Increment( int& iValue )
{
iValue++;
}
int iVariable = 0;
boost::function< void () > fIncrementMyVariable = boost::bind( &Increment, boost::ref( iVariable ));
fIncrementMyVariable();
This Dr. Dobbs article has some info.
Hope this is right, and helpful. :)
auto fIncrement = [&iVariable]{ Increment(iVariable);};reference_wrapper<T> is an immensely useful and simple library. Internally the reference_wrapper<T> stores a pointer to T. But the interface it exposes does not contain any pointer notation.
reference_wrapper<T> can be stored in a STL container.reference_wrapper<T>, pointers by references and T->f() by T.f() wherever possible (ofcourse pointers need to be stored for deleting a heap-allocated objects, but for memory management Boost Pointer Containers are quite useful).Example:
class A
{
//...
};
class B
{
public:
void setA(A& a)
{
a_ = boost::ref(a); // use boost::cref if using/storing const A&
}
A& getA()
{
return a_;
}
B(A& a): a_(a) {}
private:
boost::reference_wrapper<A> a_;
};
int main()
{
A a1;
B b(a1);
A a2;
b.setA(a2);
return 0;
}
Here I have used the boost implementation of reference wrapper, but C++0x standard is going to have it too. See also http://aszt.inf.elte.hu/~gsd/halado_cpp/ch11.html#Bind-ref
