部分模板绑定，创建新模板作为类型 [英] Partial template binding, create new template as type

问题描述

是否存在将模板部分绑定到参数类型的方法?例如，我有以下模板:

template<typename T, typename Q> struct generic { };

我还有另一个模板，它以模板类为参数，希望能够用第一种类型创建它的实例:

template<typename T, template<typename> class Impl>
struct wrapper {
    Impl<T> foo;
};

这将接受一个简单的模板，如template<typename T>而不进行任何更改.我现在想做的是部分绑定generic模板，仅指定Q并将其传递给wrapper.组成一些语法，也许像这样:

template<typename T> bound = generic<T,some_type>;

我知道我几乎可以通过继承得到我想要的东西:

template<typename T> bound : public generic<T,some_type> { };

我希望能避免这种情况，因为它会导致基类中定义的构造函数和运算符出现问题.

解决方案

在C ++ 11中，您可以使用模板别名

template<class X>
using Bind_CPP11 = generic<X, Y>;

template<class X, template<class> class Impl>
struct wrapper_CPP11
{
    Impl<X> foo;
};

在C ++ 98/03中，您可以使用简单的 类组成 (I不会在这里使用继承)

template<class X>
struct Bind_CPP03
{
    typedef generic<X, Y> type;
};

template<class X, template<class> class Impl>
struct wrapper_CPP03
{
    typename Impl<X>::type foo;
//  ^^^^^^^^ to extract dependent type
};

实时示例 ./p>

Is there some way to partially bind a template to parameter types? For example, I have the following template:

template<typename T, typename Q> struct generic { };

And I have another template which takes a template class as a parameter, expecting to be able to create instances of it with the first type:

template<typename T, template<typename> class Impl>
struct wrapper {
    Impl<T> foo;
};

This would accept a simple template like template<typename T> without changes. What I want to do now is partially bind the generic template, specifying only Q and passing it to wrapper. Making up some syntax, perhaps something like this:

template<typename T> bound = generic<T,some_type>;

I know I can almost get what I want using inheritance:

template<typename T> bound : public generic<T,some_type> { };

I am hoping though to avoid this though as it causes issues with constructors and operators defined in the base class.

解决方案

In C++11 you can use template aliases

template<class X>
using Bind_CPP11 = generic<X, Y>;

template<class X, template<class> class Impl>
struct wrapper_CPP11
{
    Impl<X> foo;
};

In C++98/03, you can use simple class composition (I would not use inheritance here)

template<class X>
struct Bind_CPP03
{
    typedef generic<X, Y> type;
};

template<class X, template<class> class Impl>
struct wrapper_CPP03
{
    typename Impl<X>::type foo;
//  ^^^^^^^^ to extract dependent type
};

Live Example.

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