ModernParadigm.hxx

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#pragma once

 
#include <concepts>
#include <cstdint>
#include <expected>
#include <span>
#include <string_view>
 
namespace tutorial {

struct Price {
  std::int64_t cents{};
  friend constexpr bool operator==(Price, Price) = default;
};

struct Quantity {
  std::int32_t value{};
  friend constexpr bool operator==(Quantity, Quantity) = default;
};

enum class ParseErr : int { empty = 1, invalid = 2, overflow = 3 };

[[nodiscard]] std::expected<Price, ParseErr> parse_price_cents(std::string_view s);

[[nodiscard]] std::int64_t sum_cents(std::span<const Price> prices) noexcept;

template <class T>
concept NamedValue = requires(T t) {
  { t.value } -> std::convertible_to<std::int32_t>;
};

template <NamedValue T>
[[nodiscard]] constexpr std::int32_t raw_qty(T t) noexcept {
  return t.value;
}
 
}  // namespace tutorial