我想创建一个模板类,该模板类为作为模板参数传递的每种类型实现print()方法。

像这样:

class Interface
{
public:
    virtual ~Interface() = default;
    virtual void print(int) = 0;
    virtual void print(double) = 0;
};
X x<int, double, Interface>;
class X具有公共(public)方法void print(),它可以工作。

整个代码如下:
#include <iostream>
#include <type_traits>

struct Printer
{
    void print(int i) {std::cout << i << std::endl; }
    void print(double d) {std::cout << d << std::endl; }
};

class Interface
{
public:
    virtual ~Interface() = default;
    virtual void print(int) = 0;
    virtual void print(double) = 0;
};

template <typename... Args>
class X;

template <typename Interface>
class X<Interface> : public Interface
{
    static_assert(std::is_abstract<Interface>::value, "Last argument should be an interface");

public:
    X(Printer printer) {}
    using Interface::print;
};

template <typename Arg, typename... Args>
class X<Arg, Args...> : public X<Args...>
{
    using Parent = X<Args...>;

public:
    using Parent::print;

    X(Printer printer_): Parent(printer), printer{printer_} {}
    void print(Arg arg) override { printer.print(arg); }

private:
    Printer printer;
};

int main()
{
    Printer printer;
    X<double, int, Interface> x(printer);
    x.print(5);
}

如您所见,class X使用Printer类,但问题是我想将Printer作为模板参数...

可能吗?怎么做?

最佳答案


抱歉,但是...我没看到问题(故事讲述者建议简化一下:将一个Printer对象放在底例中)

template <typename...>
class X;

template <typename Printer, typename Interface>
class X<Printer, Interface> : public Interface
 {
   static_assert(std::is_abstract<Interface>::value,
                 "Last argument should be an interface");

   public:
      X (Printer p0) : printer{p0}
       { }

      using Interface::print;  // why?

   protected:
      Printer printer;
 };

template <typename Printer, typename Arg, typename... Args>
class X<Printer, Arg, Args...> : public X<Printer, Args...>
 {
   using Parent = X<Printer, Args...>;

   public:
      using Parent::print;
      using Parent::printer;

      X(Printer printer_): Parent{printer_} {}

      void print(Arg arg) override { printer.print(arg); }
 };

// ....

X<Printer, double, int, Interface> x(printer);
主题外:注意:您正在使用未初始化的printer
X(Printer printer_): Parent(printer), printer{printer_} {}
我想你应该写Parent(printer_)

关于c++ - 模板类使用参数包时如何传递其他模板参数?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/58712888/

10-11 22:10
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