cpp-useful-iterators/include/iterator/detail/default_constructible_function_proxy.h

//
//  default_constructible_function_proxy.h
//  iterator
//
//  Created by Sam Jaffe on 4/1/23.
//  Copyright © 2023 Sam Jaffe. All rights reserved.
//

#include <optional>

#include <iterator/detail/macro.h>

namespace iterator::detail {
template <typename F, typename = void>
class default_constructible_function_proxy {
public:
  default_constructible_function_proxy() = default;
  default_constructible_function_proxy(F func) : func_(func) {}

  template <typename... Args> decltype(auto) operator()(Args &&... args) const {
    if (!func_) { throw; }
    return std::invoke(*func_, FWD(args)...);
  }

private:
  std::optional<F> func_;
};

template <typename F>
class default_constructible_function_proxy<
    F, std::enable_if_t<std::is_default_constructible_v<F>>> {

public:
  default_constructible_function_proxy() = default;
  default_constructible_function_proxy(F func) : func_(func) {}

  template <typename... Args> decltype(auto) operator()(Args &&... args) const {
    return std::invoke(func_, FWD(args)...);
  }

private:
  F func_;
};
}

#include <iterator/detail/undef.h>