不限制递归深度，就可以对编译器发起DoS attack

MSVC的demo可以用这个程序（https://itecnote.com/tecnote/c-template-metaprogramming-recursion-up-limits/）
VS2022的/std:c++20只能编译Sum<499>::value，不能编译Sum<500>::value，跟帖子里说的VC9一样。

template <int N> class Sum {
public:
  enum { value = N + Sum<N - 1>::value };
};

template <> class Sum<0> {
public:
  enum { value = 0 };
};

int main() {
  printf("%d\n", Sum<499>::value);

The standard recommends an implementation support at least 1024 levels of recursive instantiation, and infinite recursion in template instantiations is undefined behavior.
https://en.cppreference.com/w/cpp/language/template_metaprogramming
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修改:z16166 FROM 221.220.168.*
FROM 221.220.168.*