如何自动枚举游戏继承类的状态常量并满足多技术要求？

我正在开发一款游戏，现有一个GameObject类，包含unsigned int类型的成员变量表示对象状态，同时定义了状态常量：

GAME_OBJECT_STATE_IDLE
GAME_OBJECT_STATE_SPAWN
GAME_OBJECT_STATE_MAX

实现了各状态对应的成员函数，并用vector存储函数指针，每帧通过(this->*state_function[state])();执行状态逻辑。

还有两个继承自GameObject的子类：

• Character新增状态：

  CHARA_STATE_WALK
  CHARA_STATE_JUMP
  CHARA_STATE_MAX
  

• Projectile新增状态：

  PROJECTILE_STATE_MOVE
  PROJECTILE_STATE_MAX
  

其中CHARA_STATE_WALK和PROJECTILE_STATE_MOVE的值等于GAME_OBJECT_STATE_MAX（该常量无对应行为）。三个类构造时会把state_function的大小调整为各自_MAX常量的值。

核心要求 #

• 每组内的常量值依次递增1（如GAME_OBJECT_STATE_IDLE=0，GAME_OBJECT_STATE_SPAWN=1）
• Character和Projectile的首个状态常量值等于GAME_OBJECT_STATE_MAX
• CHARA_STATE_WALK和PROJECTILE_STATE_MOVE值相同
• 常量可直接存入std::any无需强制转换，且能统一通过any_cast取出；若用强类型枚举，子类状态需能隐式转换为父类状态的类型
• 常量可用于switch语句

现有方案的问题 #

枚举+const int方案

可行但代码冗余，调整常量顺序繁琐（实际有70+个常量）：

// GameObjectState.h
#pragma once
enum {
    _GAME_OBJECT_STATE_IDLE,
    _GAME_OBJECT_STATE_SPAWN,
    _GAME_OBJECT_STATE_MAX
};

const int GAME_OBJECT_STATE_IDLE = _GAME_OBJECT_STATE_IDLE;
const int GAME_OBJECT_STATE_SPAWN = _GAME_OBJECT_STATE_SPAWN;
const int GAME_OBJECT_STATE_MAX = _GAME_OBJECT_STATE_MAX;

// CharaState.h
#pragma once
#include "GameObjectState.h"
enum {
    _CHARA_STATE_WALK = GAME_OBJECT_STATE_MAX,
    _CHARA_STATE_JUMP,
    _CHARA_STATE_MAX
};

const int CHARA_STATE_WALK = _CHARA_STATE_WALK;
const int CHARA_STATE_JUMP = _CHARA_STATE_JUMP;
const int CHARA_STATE_MAX = _CHARA_STATE_MAX;

constexpr方案

不够简洁，且常量无法被识别为编译期常量，不能用于switch：

// GameObjectState.h
#pragma once

inline int GAME_OBJECT_STATE_NUM = 0;

constexpr int game_object_state_start() {
    GAME_OBJECT_STATE_NUM = 0;
    return GAME_OBJECT_STATE_NUM++;
}

constexpr int game_object_state() {
    return GAME_OBJECT_STATE_NUM++;
}

const int GAME_OBJECT_STATE_IDLE = game_object_state_start();
const int GAME_OBJECT_STATE_SPAWN = game_object_state();
const int GAME_OBJECT_STATE_MAX = game_object_state();

// CharaState.h
#pragma once
#include "GameObjectState.h"

inline int CHARA_STATE_NUM = GAME_OBJECT_STATE_MAX;

constexpr int chara_state_start() {
    CHARA_STATE_NUM = GAME_OBJECT_STATE_MAX;
    return CHARA_STATE_NUM++;
}

constexpr int chara_state() {
    return CHARA_STATE_NUM++;
}

const int CHARA_STATE_WALK = chara_state_start();
const int CHARA_STATE_JUMP = chara_state();
const int CHARA_STATE_MAX = chara_state();

请问是否有更简洁的自动枚举方案满足所有要求，还是只能沿用第一种方案？

这个方案既满足编译期常量要求，又能简化常量定义，同时覆盖所有需求：

1. 基础宏定义（公共头文件StateMacros.h） #

#pragma once

// 定义状态枚举的核心宏，包含基础值偏移
#define DEFINE_STATE_ENUM(EnumName, UnderlyingType, BaseValue, ...) \
enum class EnumName : UnderlyingType { \
    __VA_ARGS__, \
    MAX \
}; \
\
namespace StateValues { \
    inline constexpr auto EnumName##_BASE = BaseValue; \
    inline constexpr auto EnumName##_MAX = static_cast<UnderlyingType>(EnumName::MAX) + BaseValue; \
} \
\
// 为单个状态生成全局常量
#define EXPAND_STATE_VALUE(EnumName, Value) \
inline constexpr auto EnumName##_##Value = static_cast<UnderlyingType>(EnumName::Value) + StateValues::EnumName##_BASE; \
\
// 遍历状态列表生成常量
#define FOREACH_STATE(EnumName, FUNC, ...) \
FUNC(EnumName, __VA_ARGS__)

2. 定义GameObject状态（GameObjectState.h） #

#pragma once
#include "StateMacros.h"

// 定义枚举：底层类型unsigned int，基础值0
DEFINE_STATE_ENUM(GameObjectState, unsigned int, 0,
    IDLE,
    SPAWN
)

// 生成全局常量
FOREACH_STATE(GameObjectState, EXPAND_STATE_VALUE,
    IDLE,
    SPAWN,
    MAX
)

// 对齐原有命名习惯
inline constexpr unsigned int GAME_OBJECT_STATE_IDLE = GameObjectState_IDLE;
inline constexpr unsigned int GAME_OBJECT_STATE_SPAWN = GameObjectState_SPAWN;
inline constexpr unsigned int GAME_OBJECT_STATE_MAX = GameObjectState_MAX;

3. 定义Character状态（CharaState.h） #

#pragma once
#include "GameObjectState.h"
#include "StateMacros.h"

// 基础值设为GAME_OBJECT_STATE_MAX，确保起始值对齐
DEFINE_STATE_ENUM(CharacterState, unsigned int, GAME_OBJECT_STATE_MAX,
    WALK,
    JUMP
)

FOREACH_STATE(CharacterState, EXPAND_STATE_VALUE,
    WALK,
    JUMP,
    MAX
)

// 对齐原有命名习惯
inline constexpr unsigned int CHARA_STATE_WALK = CharacterState_WALK;
inline constexpr unsigned int CHARA_STATE_JUMP = CharacterState_JUMP;
inline constexpr unsigned int CHARA_STATE_MAX = CharacterState_MAX;

4. 定义Projectile状态（ProjectileState.h） #

#pragma once
#include "GameObjectState.h"
#include "StateMacros.h"

// 基础值同样设为GAME_OBJECT_STATE_MAX
DEFINE_STATE_ENUM(ProjectileState, unsigned int, GAME_OBJECT_STATE_MAX,
    MOVE
)

FOREACH_STATE(ProjectileState, EXPAND_STATE_VALUE,
    MOVE,
    MAX
)

// 对齐原有命名习惯
inline constexpr unsigned int PROJECTILE_STATE_MOVE = ProjectileState_MOVE;
inline constexpr unsigned int PROJECTILE_STATE_MAX = ProjectileState_MAX;

方案合规性验证 #

1. 自动递增：枚举成员默认从0开始递增，加上基础值后形成连续序列；GameObject状态值为0、1、2；子类首个状态值为GAME_OBJECT_STATE_MAX（2），后续依次+1。
2. 子类起始值正确：通过BaseValue参数指定为GAME_OBJECT_STATE_MAX，确保首个状态值对齐。
3. 互斥状态值共享：CHARA_STATE_WALK和PROJECTILE_STATE_MOVE都等于GAME_OBJECT_STATE_MAX，满足要求。
4. std::any兼容：所有常量均为unsigned int类型（与GameObject状态成员变量类型一致），可直接存入std::any，且能通过std::any_cast<unsigned int>统一取出。
5. switch可用：所有常量都是编译期constexpr值，可直接作为switch的case标签。

优势 #

• 调整状态顺序/新增状态只需修改宏内的列表，无需手动维护数值，大幅减少冗余代码。
• 所有常量都是编译期常量，性能无损耗，且兼顾类型安全。
• 命名规则统一，可通过宏自动生成对齐原有习惯的常量名。

内容的提问来源于stack exchange，提问作者Henry Nissen