问题描述

template<>
class A{
//some class data
};

这种代码我见过很多次了.上面代码中template<>的作用是什么?在哪些情况下我们需要强制使用它?

I have seen this kind of code many times. what is the use of template<> in the above code? And what are the cases where we need mandate the use of it?

推荐答案

template<> 告诉编译器遵循模板特化，特别是完全特化.通常，class A 应该是这样的:

template<> tells the compiler that a template specialization follows, specifically a full specialization. Normally, class A would have to look something like this:

template<class T>
class A{
  // general implementation
};

template<>
class A<int>{
  // special implementation for ints
};

现在，每当使用 A 时，都会使用专用版本.你也可以用它来专门化函数:

Now, whenever A<int> is used, the specialized version is used. You can also use it to specialize functions:

template<class T>
void foo(T t){
  // general
}

template<>
void foo<int>(int i){
  // for ints
}

// doesn't actually need the <int>
// as the specialization can be deduced from the parameter type
template<>
void foo(int i){
  // also valid
}

通常情况下，你不应该专门化函数，因为简单的重载通常被认为是优越的:

Normally though, you shouldn't specialize functions, as simple overloads are generally considered superior:

void foo(int i){
  // better
}

<小时>

现在，为了让它显得矫枉过正，以下是一个部分专业化:

template<class T1, class T2>
class B{
};

template<class T1>
class B<T1, int>{
};

与完全特化的工作方式相同，只是当第二个模板参数是 int(例如，B、B 等).

Works the same way as a full specialization, just that the specialized version is used whenever the second template parameter is an int (e.g., B<bool,int>, B<YourType,int>, etc).

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