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

#pragma once

#include <compare>

/**
 * @brief Generator-macro for creating instant tri-bools, a boolean-like type
 * that has a "True" state, a "False" state, and a "Maybe"/"Indeterminate"
 * state. {@see boost::tribool} for an example of this functionality.
 *
 * TriBool types obey the following rules of behavior (with T := True,
 * F := False, M := Maybe):
 *
 * Unary operators operate as follows:
 * | op \ in | T | F | M |
 * |---------|---|---|---|
 * |  bool() | T | F | T |
 * |       ! | F | T | M |
 * |---------|---|---|---|
 *
 * AND operates as follows:
 * |   | T | F | M |
 * |---|---|---|---|
 * | T | T | F | T |
 * | F | F | F | F |
 * | M | T | F | M |
 * |---|---|---|---|
 *
 * OR operates as follows:
 * |   | T | F | M |
 * |---|---|---|---|
 * | T | T | T | T |
 * | F | T | F | M |
 * | M | T | M | M |
 * |---|---|---|---|
 *
 * @param TypeName the name of the class being declared
 * @param True the name of the truthy enumeration
 * @param False the name of the falsy enumeration
 * @param Maybe the name of the indeterminate enumeration
 */
#define JVALIDATE_TRIBOOL_TYPE(TypeName, True, False, Maybe)                                       \
  class TypeName {                                                                                 \
  public:                                                                                          \
    enum Enum { True, False, Maybe };                                                              \
                                                                                                   \
  private:                                                                                         \
    Enum state_;                                                                                   \
                                                                                                   \
  public:                                                                                          \
    /* Translate a boolean into a tribool value, will never be Maybe */                            \
    constexpr TypeName(bool state) : state_(state ? True : False) {}                               \
    constexpr TypeName(Enum state) : state_(state) {}                                              \
                                                                                                   \
    /* Convert to enum for use in switch() statements */                                           \
    constexpr Enum operator*() const { return state_; }                                            \
    /* Convert to bool for use in if()/while() statements, requires static_cast otherwise */       \
    constexpr explicit operator bool() const { return state_ != False; }                           \
                                                                                                   \
    /* Inverts the tribool's value if it is already a concrete boolean type */                     \
    friend constexpr TypeName operator!(TypeName val) {                                            \
      if (val.state_ == Maybe) {                                                                   \
        return Maybe;                                                                              \
      }                                                                                            \
      return val.state_ == False ? True : False;                                                   \
    }                                                                                              \
                                                                                                   \
    /* Combines two tribools as if performing boolean-OR */                                        \
    friend constexpr TypeName operator|(TypeName lhs, TypeName rhs) {                              \
      if (lhs.state_ == True || rhs.state_ == True) {                                              \
        return True;                                                                               \
      }                                                                                            \
      if (lhs.state_ == Maybe || rhs.state_ == Maybe) {                                            \
        return Maybe;                                                                              \
      }                                                                                            \
      return False;                                                                                \
    }                                                                                              \
                                                                                                   \
    /* Combines two tribools as if performing boolean-AND */                                       \
    friend constexpr TypeName operator&(TypeName lhs, TypeName rhs) {                              \
      if (lhs.state_ == False || rhs.state_ == False) {                                            \
        return False;                                                                              \
      }                                                                                            \
      if (lhs.state_ == Maybe && rhs.state_ == Maybe) {                                            \
        return Maybe;                                                                              \
      }                                                                                            \
      return True;                                                                                 \
    }                                                                                              \
                                                                                                   \
    constexpr TypeName & operator&=(TypeName rhs) { return *this = *this & rhs; }                  \
    constexpr TypeName & operator|=(TypeName rhs) { return *this = *this | rhs; }                  \
                                                                                                   \
    friend constexpr auto operator==(TypeName lhs, TypeName::Enum rhs) {                           \
      return static_cast<int>(lhs.state_) == static_cast<int>(rhs);                                \
    }                                                                                              \
    friend constexpr auto operator!=(TypeName lhs, TypeName::Enum rhs) {                           \
      return static_cast<int>(lhs.state_) != static_cast<int>(rhs);                                \
    }                                                                                              \
    friend constexpr auto operator<=>(TypeName lhs, TypeName rhs) {                                \
      return static_cast<int>(lhs.state_) <=> static_cast<int>(rhs.state_);                        \
    }                                                                                              \
  }