Question

Suppose I have some template class forward declared and I want to typedef a shared pointer to it. How would I do this?

template<typename T> class Arg;
typedef std::tr1::shared_ptr<Arg> ArgPtr; // Compiler error

Answer 1

You also probably want template typedef. Read up on Sutter’s article.

In C++03, you need a hack as:

template <typename Arg> struct ArgPtr {
     typedef std::shared_ptr<Arg> ArgPtrType;
};

In C++11, you can use template aliasing directly with the using keyword:

template <typename T>
using ArgPtrType = std::shared_ptr<Arg<T>>;