模板部分专业化 - 任何现实世界的例子？ [英] Template Partial Specialization - any real-world example?

问题描述

我在思考部分专业化。虽然我理解这个想法，我还没有看到这种技术的任何真实世界的使用。 完全专业化在 STL 中的许多地方使用，因此我没有问题。你能告诉我一个现实世界的例子，使用部分专业化吗？如果示例是 STL ，那将是优越的！

I am pondering about partial specialization. While I understand the idea, I haven't seen any real-world usage of this technique. Full specialization is used in many places in STL so I don't have a problem with that. Could you educate me about a real-world example where partial specialization is used? If the example is in STL that would be superior!

推荐答案

C ++ 0x带有 unique_ptr ，它替代了将被弃用的 auto_ptr 。

C++0x comes with unique_ptr which is a replacement for auto_ptr which is going to be deprecated.

如果对数组类型使用 unique_ptr ，则使用 delete [] 来释放它，并提供 operator [] 等。如果你使用非数组类型，它使用 delete 。这需要部分模板专门化，例如

If you use unique_ptr with an array type, it uses delete[] to free it, and to provide operator[] etc. If you use it with a non-array type, it uses delete. This needs partial template specialization like

template<typename T>
struct my_unique_ptr { ... };

template<typename T>
struct my_unique_ptr<T[]> { ... };

另一种用法（尽管非常有问题）是 std :: vector< bool ，Allocator> 。 bool专门化使用空间优化将bools包装成单独的位

Another use (although a very questionable) is std::vector<bool, Allocator> in the standard library. The bool specialization uses a space optimization to pack bools into individual bits

template<typename T, typename Allocator = std::allocator<T> >
struct vector { ... };

template<typename Allocator>
struct vector<bool, Allocator> { ... };

另一种用法是使用 std :: iterator_traits< T> 。迭代器需要定义嵌套的typedefs value_type ，引用和其他的正确的类型（对于一个const迭代器，例如，code> reference 通常是 T const& ），因此算法可以使用它们进行工作。主模板依次使用迭代器类型的类型成员

Yet another use is with std::iterator_traits<T>. Iterators are required to define the nested typedefs value_type, reference and others to the correct types (for a const iterator, reference would usually be T const&, for example) so algorithms may use them for their work. The primary template uses type-members of the iterator type in turn

template<typename T>
struct iterator_traits { 
  typedef typename T::value_type value_type; 
  ...
};

对于指针，这当然不起作用。

For pointers, that of course doesn't work. There is a partial specialization for them

template<typename T>
struct iterator_traits<T*> {
  typedef T value_type;
  ...
};

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