Typedef不指定模板参数的模板类 [英] Typedef a template class without specifying the template parameters

问题描述

我试图typedef unordered_map或std :: map，取决于是否有TR1库可用。但是我不想指定模板参数。从我到目前为止，typedef的模板没有参数是不可能的，直到官方的c ++ 0x标准可用。那么任何人都知道一个优雅的解决方法吗？

I'm trying to typedef either an unordered_map or std::map depending whether there are TR1 libraries available. But I don't want to specify the template parameters. From what i've read so far, typedef'ing templates without arguments is not possible until official c++0x standard is available. So does anyone know an elegant workaround for this?

#ifdef _TR1
#include <unordered_map> 
typedef std::tr1::unordered_map MyMap; //error C2976: too few template arguments
#else
#include <map> 
typedef std::map MyMap; //error C2976: too few template arguments
#endif

推荐答案

我看到这样做的方式是将typedef包装在template-struct中：

The way I've seen this done is to wrap the typedef in a template-struct:

template<typename KeyType, typename MappedType>
struct myMap
{
#ifdef _TR1
    typedef std::tr1::unordered_map<KeyType, MappedType> type;
#else
    typedef std::map<KeyType, MappedType> type;
#endif
};

然后在您的代码中调用它：

Then in your code you invoke it like so:

myMap<key, value>::type myMapInstance;

这可能比你想要的更繁琐，但我相信它满足了C ++的当前状态。

It may be a little more verbose than what you want, but I believe it meets the need given the current state of C++.

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