如何設置boost :: optional回到未初始化的狀態？

Question

如何「重設」/「取消」boost::optional？

optional<int> x; 

if(x) 
{ 
    // We won't hit this since x is uninitialized 
} 
x = 3; 
if(x) 
{ 
    // Now we will hit this since x has been initialized 
} 
// What should I do here to bring x back to uninitialized state? 
if(x) 
{ 
    // I don't want to hit this 
} 

Answer 1

x = boost::none; 

Answer 2

一個簡單的方法是這樣的：

x = optional<int>(); //reset to default 

或者乾脆：

x.reset(); 

它破壞的電流值，離開這個未初始化（默認）。