Thread: C++0x Concepts fall

Meh, it has two different purposes.
1) Import a specific type into the a namespace (ie use std::cout).
3) Create a type alias (ie template<typename T> using Vec = std::vector).

Originally Posted by Elysia

Meh, it has two different purposes.
1) Import a specific type into the global namespace (ie use std::cout).

Into any namespace. You can do this:

Code:

namespace foo { void x(); }
namespace bar { using foo::x; }
void f() { bar::x(); }

This is quite often useful, e.g. many Boost libraries define most of their symbols in a library-specific namespace and lift a few important names into the boost namespace.

2) Create a namespace alias (ie using l = boost::lambda).

No, you do that using namespace:

Code:

namespace ll = boost::lambda;
namespace fs = boost::filesystem;

3) Create a type alias (ie template<typename T> using Vec = std::vector).

That one is new in C++0x.

There's more.
4) Make names from a base class visible in the derived class despite overloading:

Code:

struct Base {
  virtual void f(int);
  virtual void f(float);
};
struct Derived : public Base {
  virtual void f(int); // Override (int) version.
  using Base::f; // But let the compiler still find the (float) version.
};

5) Change access of inherited elements, especially inherited from private bases:

Code:

class Whatever : private std::vector<int> {
public:
  typedef std::vector<int>::iterator iterator;
  typedef std::vector<int>::const_iterator const_iterator;
  using std::vector<int>::begin;
  using std::vector<int>::end;
};

Re 2): Oh yes, my bad. I don't know what I was thinking...
And I forgot 1). I've seen it, of course.