lazy.h

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/*******************************************************************\
 
Module: Util
 
Author: Romain Brenguier, romain.brenguier@diffblue.com
 
\*******************************************************************/
 
#ifndef CPROVER_UTIL_LAZY_H
#define CPROVER_UTIL_LAZY_H
 
#include <functional>
#include <optional>
 
template <typename valuet>
class lazyt
{
public:
  static lazyt from_fun(std::function<valuet()> fun)
  {
    return lazyt{std::move(fun)};
  }

  valuet force()
  {
    if(value)
      return *value;
    value = evaluation_function();
    return *value;
  }
 
private:
  std::optional<valuet> value;
  std::function<valuet()> evaluation_function;
 
  explicit lazyt(std::function<valuet()> fun)
    : evaluation_function(std::move(fun))
  {
  }
};

template <typename funt>
auto lazy(funt fun) -> lazyt<decltype(fun())>
{
  return lazyt<decltype(fun())>::from_fun(std::move(fun));
}
 
#endif // CPROVER_UTIL_LAZY_H