json-validator/include/jvalidate/detail/out.h

#pragma once

#include <type_traits>
#include <utility>
#include <variant>

namespace jvalidate::detail {
template <typename T> class out;

constexpr struct discard_out_t {
} discard_out;

template <typename T> class out {
private:
  T * ref_ = nullptr;

public:
  out() = default;
  out(discard_out_t) {}
  out(T & ref) : ref_(&ref) {}

  explicit operator bool() const { return ref_; }

  template <typename U>
  requires std::is_constructible_v<T, U>
  void operator=(U && val) {
    if (ref_) {
      *ref_ = std::forward<U>(val);
    }
    return *this;
  }
};

template <typename T>
requires(std::is_same_v<T, std::decay_t<T>>) class inout {
private:
  std::variant<T, T *> ref_;

public:
  inout(T && value) : ref_(std::move(value)) {}
  inout(T & ref) : ref_(&ref) {}

  operator T const &() const {
    struct {
      T const & operator()(T const & in) const { return in; }
      T const & operator()(T * in) const { return *in; }
    } visitor;
    return std::visit(visitor, ref_);
  }

  template <typename U>
  requires std::is_constructible_v<T, U> T const & operator=(U && val) {
    struct {
      U && val;
      void operator()(T & in) const { in = std::forward<U>(val); }
      void operator()(T * in) const { *in = std::forward<U>(val); }
    } visitor{std::forward<U>(val)};
    std::visit(visitor, ref_);
    return static_cast<T const &>(*this);
  }
};
}