如何将 boost::optional 设置回未初始化状态？

Question

如何“重置”/“取消设置”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

或者简单地说：

x.reset(); 

它会破坏当前值，保持未初始化（默认）。