C++(17)：使用visit访问variant

把variant类型作为参数传递给一个函数，并不像想象的那么简单：

#include 
#include 
#include 
using namespace std;
 
void pOut(variant<int, double, string>& v)
{
	if(auto p = get_if<int>(&v))
	{
		cout<<"v is int, and value is "<<*p<
	}
	else if(auto p = get_if<double>(&v))
	{
		cout<<"v is double, and value is "<<*p<
	}
	else if(auto p = get_if(&v))
	{
		cout<<"v is string, and value is "<<*p<
	}
}
 
int main()
{
	variant<int, double, string> v1{8}, v2{3.14}, v3{"hi"};
	pOut(v1);
	pOut(v2);
	pOut(v3);
	return 0;
}

运行程序输出：
v is int, and value is 8
v is double, and value is 3.14
v is string, and value is hi

可以看到需要在函数里对variant当前的类型进行检查，