c++ - 为什么编译器提示 f() 不可见？

Question

#include <iostream>

using namespace std;

template <size_t N>
typename enable_if<(N > 1), void>::type f(){
    cout << N - 1 << ' ';
    f<N - 1>();
}
template <size_t N>
typename enable_if<N == 1, void> ::type f() {
    cout << 1;
}
int main() {
    f<4>();
}

编译器在第 8 行报错:

f< N - 1 >();

Call to function f that is neither visible in the template definition nor found by ADL.

Answer 1

反转函数定义的顺序。

#include <iostream>
#include <type_traits>

using namespace std;

template <size_t N>
typename enable_if<N == 1, void> ::type f() {
    cout << 1;
}
template <size_t N>
typename enable_if<(N > 1), void>::type f(){
    cout << N - 1 << ' ';
    f<N - 1>();
}
int main() {
    f<4>();
}

输出:

$ ./a.out
3 2 1 1