<分区>
类(class)foo包含一个私有(private)元组成员。我想使用 getElement<I>() 获取对此元组元素的引用.我找到了这个解决方案，但是当对象被传递给另一个类的构造函数时它不起作用 bar :
#include <tuple>
template<class... Args>
class foo {
std::tuple<Args...> tup_;
public:
foo(Args... args) : tup_ {args...} {};
template<size_t I>
const typename std::tuple_element<I, std::tuple<Args...>>::type &
getElement() const {return std::get<I>(tup_);}
};
template<class T>
class bar;
template<class T, class U>
class bar<foo<T,U>> {
public:
bar(foo<T,U> f) {
auto j = f.getElement<0>(); // this is an ERROR!!! Line 22
}
};
int main()
{
foo<int, char> f(12,'c');
auto j = f.getElement<0>(); // but this is OK!
bar<decltype(f)> b(f);
return 0;
}
编译器输出:
main.cpp: In constructor 'bar<foo<T, U> >::bar(foo<T, U>)':
main.cpp:22:33: error: expected primary-expression before ')' token
auto j = f.getElement<0>(); // this is an ERROR!!!
^
main.cpp: In instantiation of 'bar<foo<T, U> >::bar(foo<T, U>) [with T = int; U = char]':
main.cpp:32:24: required from here
main.cpp:22:29: error: invalid operands of types '<unresolved overloaded function type>' and 'int' to binary 'operator<'
auto j = f.getElement<0>(); // this is an ERROR!!!