使用非专用模板化类型作为模板参数

Question

这是我想要实现的运行示例：

#include <iostream>
#include <string>
#include <typeinfo>

template <class T> 
struct print
{
    static void function( T thing)
    {
        std::cout << thing << std::endl;
    }
};

template <class T>
struct printMore
{
    static void function( T thing )
    {
        std::cout << thing << " and more" << std::endl;
    }
};

struct dynamicBase
{
    const char* m_value;

    size_t getType()
    {
        switch( *m_value )
        {
        case '0': //the string is going to be a small script, the type returned is known during execution but not at compile time
            return typeid( int ).hash_code();
        case '1':
            return typeid( float ).hash_code();
        }
        return typeid( const char* ).hash_code();
    }

    template<class T>
    T* tryGetValue()
    {
        if( getType() == typeid( T ).hash_code() )
            return (T*) ( &( m_value[1] ) ); //dumb example, actually I'll evaluate the string as script and return a value based on that
        else
            return nullptr;
    }

    void applyPrint(  )
    {
        if( int* t = tryGetValue<int>() )
            print<int>::function( *t ); //I can cout an int so this line compile
        else if( float* t = tryGetValue<float>() )
            print<float>::function( *t ); //I can cout a float so this one too
        else
            print<const char*>::function( *tryGetValue<const char*>() ); //same
    }
    void applyPrintMore()
    {
        if( int* t = tryGetValue<int>() )
            printMore<int>::function( *t ); 
        else if( float* t = tryGetValue<float>() )
            printMore<float>::function( *t );
        else
            printMore<const char*>::function( *tryGetValue<const char*>() ); //same
    }

    //.... applyprintPretty, applyprintInRed, applyprintInBlue, .....
};

int main()
{
    dynamicBase d;
    d.m_value = "0a\0\0\0";
    d.applyPrint(); //97 == ascii value of 'a'

    __asm {nop}; //for breakpoint purpose
}

一开始我虽然可以使用这样的模板：

    template<class myFunctionClass>
    void applyPrint(  )
   {
        if( int* t = tryGetValue<int>() )
            myFunctionClass<int>::function( *t ); 
        else if( float* t = tryGetValue<float>() )
            myFunctionClass<float>::function( *t ); 
        else
            myFunctionClass<const char*>::function( *tryGetValue<const char*>() ); 
    }

然后意识到我的错误（在您为模板类型提供模板参数之前，模板类型不是类型）。但是有没有办法重构此代码，所以我没有15个applyStuff函数？（我做错了，不是吗？）

Answer 1

您正在寻找模板模板参数：

template<template <typename> class myFunctionClass>
void applyPrint(  )
{
        if( int* t = tryGetValue<int>() )
            myFunctionClass<int>::function( *t ); 
        else if( float* t = tryGetValue<float>() )
            myFunctionClass<float>::function( *t ); 
        else
            myFunctionClass<const char*>::function( *tryGetValue<const char*>() ); 
}

您可以在此处找到参考：“cppreference.com - Template 模板参数”。