模板类中函数的模板参数

Question

I have situation like this

template<class T> class Vector {
  T *data;
  uint _size, _counter;
public:
  class Iterator;
  template<template<class> class C> Vector(typename C<T>::Iterator it1,
                                           typename C<T>::Iterator it2) {
    data = NULL;
    _size = _counter = 0;
    for(typename C<T>::Iterator it = it1; it != it2 && it != end(); it++)
      push(*it);
  }
};

that is my own Vector class and the constructor mimics behaviour of vector (u can construct it with range of data supplied using interators) but add requirement that the container is to be template of the same type as the one under construction. I get error

5.cpp:16:36: error: no matching function for call to 'Vector::Vector(Vector::Iterator, Vector::Iterator)' 5.cpp:16:36: note: candidates are: In file included from 5.cpp:2:0:

5.hpp:17:37: note: template class typedef C C> Vector::Vector(typename C::Iterator, typename C::Iterator)

5.hpp:17:37: note: template argument deduction/substitution failed:

5.cpp:16:36: note: couldn't deduce template parameter 'template class typedef C C' In file included from 5.cpp:2:0:

5.hpp:11:3: note: Vector::Vector() [with T = int]

5.hpp:11:3: note: candidate expects 0 arguments, 2 provided

5.hpp:7:25: note: Vector::Vector(const Vector&)

5.hpp:7:25: note: candidate expects 1 argument, 2 provided

Need some help in here.

Answer 1

In:

 template<template<class> class C> Vector(typename C<T>::Iterator it1,
                                           typename C<T>::Iterator it2) 

the compiler does not deduce type C from typename C<T>::Iterator because it is what is called nondeduced context .

See §14.8.2.4 Deducing template arguments from a type [temp.deduct.type]:

4 The nondeduced contexts are:

— The nested-name-specifier of a type that was specified using a qualified-id.

— A type that is a template-id in which one or more of the template-arguments is an expression that references a template-parameter.