C++模拟Rust实现简易的惰性求值

#pragma once

#include
#include

template
class Lazy;

template
class Lazy
{
private:
  using FuncType = std::function;
public:
  explicit Lazy(FuncType&& func) noexcept
    :m_func(std::forward(func)) {}
  template const RType& value(Args&& ...args) noexcept {
    if(!m_value.has_value()) {
      m_value.emplace(m_func(std::forward(args)...));
    }
    return m_value.value();
  } 
private:
  FuncType m_func;
  std::optional m_value;
};

调用：