如何设置boost :: optional回到未初始化的状态？

Question

如何“重设”/“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

一个简单的方法是这样的：

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

或者干脆：

x.reset(); 

它破坏的电流值，离开这个未初始化（默认）。