C++可变模板:gcc和nvcc/intel中的不同优先级

C++ variadic template: different priorities in gcc and nvcc/intel

本文关键字：intel 优先级 nvcc gcc C++      更新时间：2023-10-16

下一个代码出现问题：

#include <iostream>
#include <functional>
using namespace std;
template<typename... Args>
inline double foo(function<double (Args...)> fun, Args... args) {
    return fun(args...);
}
template<typename... Args, typename... ArgsTmp>
double foo(function<double (Args...)> fun, ArgsTmp... args) {
    return foo(fun, 1., args...);
}
int main() {
    function<double (double, double, double)> fun = [&](double x, double y, double z) -> double {
        return x+y+z;
    };
    cout << foo(fun) << endl;
}

当我用gcc编译它时，一切都很好。但是，如果我试图用intel或nvcc-7.5编译它（这实际上是我的目标），我会得到以下错误：

more than one instance of overloaded function "foo" matches the argument list:
            function template "double foo(std::vector<limits, std::allocator<limits>>, std::function<double (Args...)>, Args...)"
            function template "double foo(std::vector<limits, std::allocator<limits>>, std::function<double (Args...)>, ArgsTmp...)"
            argument types are: (std::vector<limits, std::allocator<limits>>, std::function<double (double, double, double)>, double, double, double)
...
1 error

有没有任何方法可以让编译器明确地知道，当Args==ArgsTmp（在第二个模板中）时，foo()的以下实现应该被拒绝？

您可以尝试SFINAE和enable_if

template<typename... Args, typename... ArgsTmp>
std::enable_if_t<!std::is_same<std::tuple<Args...>,
                               std::tuple<ArgsTmp...>>::value,
                 double>
foo(function<double (Args...)> fun, ArgsTmp... args) {
    return foo(fun, 1., args...);
}

您可以考虑参数的数量：

#include <iostream>
#include <functional>
#include <type_traits>
template<typename... Args>
inline double foo(std::function<double (Args...)> fun, Args... args) {
    return fun(args...);
}
// Only considered, if the number of arguments is less than the number
// of expected arguments (accepting any number of arguments may lead 
// to infinite recursion).
template<typename... Args, typename... ArgsTmp>
inline typename std::enable_if<sizeof...(ArgsTmp) < sizeof...(Args), double>::type
foo(std::function<double (Args...)> fun, ArgsTmp... args) {
    return foo(fun, 1., args...);
}
int main()
{
    // A shorter variant
    std::function<double (double)> fun = [&](double x) -> double {
        return x;
    };
    std::cout << foo(fun) << std::endl;
    std::cout << foo(fun, 2.0) << std::endl;
    // error: no matching function for call to ‘foo(std::function<double(double)>&, double, double)’
    // std::cout << foo(fun, 3.0, 4.0) << std::endl;
}
相关文章：