c++ - 调用模板函数出错

Question

我开始使用 boost::any我正在尝试定义一个给定 boost::any 的函数参数(最初是一个 std::function 对象)将其转换回 std::function .

#include <iostream>
#include <functional>
#include <boost/any.hpp>

using namespace std;
typedef function<int(int)> intT;

template <typename ReturnType, typename... Args>
std::function<ReturnType(Args...)> converter( boost::any anyFunction) {
    return boost::any_cast<function<ReturnType(Args...)>> (anyFunction);
}

int main()
{
    intT f = [](int i) {return i; };
    boost::any anyFunction = f;
    try
    {
        intT fun = boost::any_cast<intT>(anyFunction);//OK!
        fun = converter(anyFunction);//ERROR!
    }
    catch (const boost::bad_any_cast &)
    {
        cout << "Bad cast" << endl;
    }
}

这是返回的错误:

1>c:\users\llovagnini\source\repos\cloudcache\cloudcache\cloudcache\memoization.cpp(9): error C2146: syntax error: missing ';' before identifier 'anyFunction'
1>  c:\users\llovagnini\source\repos\cloudcache\cloudcache\cloudcache\helloworld.cpp(16): note: see reference to function template instantiation 'std::function<int (void)> converter<int,>(boost::any)' being compiled
1>c:\users\llovagnini\source\repos\cloudcache\cloudcache\cloudcache\memoization.cpp(9): error C2563: mismatch in formal parameter list
1>c:\users\llovagnini\source\repos\cloudcache\cloudcache\cloudcache\memoization.cpp(9): error C2298: missing call to bound pointer to member function

你能帮我理解我哪里错了吗？

更新我解决了括号问题，但知道编译器会提示，因为我调用了 converter没有指定任何类型......有什么方法可以保持它的通用性？不指定 converter<int,int> 对我的申请非常重要

Answer 1

你...忘记添加括号:

return boost::any_cast<std::function<ReturnType(Args...)> >(anyFunction);

接下来，您无法推导模板参数，因此您必须指定它们:

fun = converter<int, int>(anyFunction);

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#include <iostream>
#include <functional>
#include <boost/any.hpp>

typedef std::function<int(int)> intT;

template <typename ReturnType, typename... Args>
std::function<ReturnType(Args...)> converter(boost::any anyFunction) {
    return boost::any_cast<std::function<ReturnType(Args...)> >(anyFunction);
}

int main()
{
    intT f = [](int i) {return i; };
    boost::any anyFunction = f;
    try
    {
        intT fun = boost::any_cast<intT>(anyFunction); // OK!
        fun = converter<int, int>(anyFunction);        // OK!
    }
    catch (const boost::bad_any_cast &)
    {
        std::cout << "Bad cast" << std::endl;
    }
}