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POtemplate typename question
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copied!<p>I have a problem with template and wondering is there a possible way to achieve what I wanted to do. Here is my question.</p> <pre><code>template <typename T> class A { public: typedef T* pointer; typedef const pointer const_pointer; A() {} template <typename D> A(const D& d) { // how can I store the D type // so I can refer it later on // outside of this function } }; </code></pre> <p>ok here is a more complete code of what I wanted to do (it might not be compilable)</p> <pre><code> class C { public: virtual ~C(){} virtual void* get_d() = 0; private: }; template <typename T, typename D> class Cimpl : public C { public: Cimpl() :t() ,d() {} Cimpl(const T& t, const D& d) :t(t) ,(d) {} void* get_d() { return &reinterpret_cast<D&>(d); } private: T t; D d; }; class B { public: B() :p(0) {} template <typename T, typename D> B(const T& t, const D& d) :p(0) { try { p = new Cimpl<T, D>(t, d); } catch(...) { d(p); } } void* get_d() { return (p != 0) ? p->get_d() : 0; } ~B() { delete p; } private: C* p; }; template <typename T> class A { struct example_d { }; public: typedef T* pointer; typedef const pointer const_pointer; A() {} template <typename D> A(const T& t) :b(t, example_d()) { } template <typename D> A(const T& t, const D& d) :b(t, d) { // how can I store the D type // so I can refer it later on // outside of this function } // not type safe...as user can cast to any type // if I can store the type user pass in previous // then I can use it back template <typename T> T* get_d() { reinterpret_cast<T*>(b.get_d()); } private: B b; }; </code></pre> <p>So I can use the class like</p> <pre><code>1)A<int> a(1);// with example_d as D 2)A<int> b(1, another_d()) // with another_d </code></pre> <p>I can change the template to take 2 parameters and use default parameter for 2nd type to be example_d. So I can achieve 1) but not 2). As I will have to code this way</p> <pre><code>A<int, another_d> b(1, another_d()); </code></pre> <p>a bit too long to type...</p>

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