随手写了一个

```
#include <boost/unordered_map.hpp>
#include <boost/function.hpp>
#include <string>

void print666()
{
printf("666\n");
}

template<class T>
using UMAP = boost::unordered_map<std::string, boost::function<T()>>;

int main()
{
UMAP<void> umap;

umap.insert(UMAP<void>::value_type("666", boost::bind(print666)));

auto res = umap.find("666");

if (res != umap.end())
{
res->second();
}
}

```

这样写的话 value 只能是同款的 Function