1
// 类型模式：is 后面跟类型名 + 变量声明
2
if (obj is string s)               // obj 是 string？顺便声明变量 s
3
    Console.WriteLine(s.Length);
4

5
// 声明模式：相当于"总是匹配"的 var
6
if (obj is var anything)           // 总是 true，anything = obj
7
    Console.WriteLine(anything);
8

9
// switch 语句中使用
10
switch (obj)
11
{
12
    case int i:
13
        Console.WriteLine($"整数: {i}");
14
        break;
15
    case string s when s.Length > 0:   // when 子句：附加条件
16
        Console.WriteLine($"非空字符串: {s}");
17
        break;
18
    case string s:
19
        Console.WriteLine("空字符串");
20
        break;
21
    case null:
22
        Console.WriteLine("null");
23
        break;
24
    default:
25
        Console.WriteLine("其他类型");
26
        break;
27
}

1
// 定义一个可解构的 Vec3
2
record Vec3(float X, float Y, float Z);
3

4
string ClassifyVector(Vec3 v) => v switch
5
{
6
    (0, 0, 0)                => "零向量",
7
    ( > 0, 0, 0)             => "X 轴正向",
8
    (0, > 0, 0)             => "Y 轴正向",
9
    (0, 0, < 0)             => "Z 轴负向",
10
    (var x, var y, var z)    => $"任意向量 ({x}, {y}, {z})"
11
};
12

13
// 配合关系模式使用
14
string DescribeHP(float hp) => hp switch
15
{
16
    <= 0     => "已死亡",
17
    < 0.25f  => "濒危",
18
    < 0.50f  => "重伤",
19
    < 0.75f  => "轻伤",
20
    >= 1.0f  => "满血",
21
    _         => "正常"
22
};

1
// 逻辑模式让组合判断更简洁
2
string ClassifyPoint(int x, int y) => (x, y) switch
3
{
4
    (0, 0)              => "原点",
5
    (0, not 0)          => "Y 轴",
6
    (not 0, 0)          => "X 轴",
7
    ( > 0 and > 0)      => "第一象限",
8
    ( < 0 and > 0)      => "第二象限",
9
    ( < 0 and < 0)      => "第三象限",
10
    ( > 0 and < 0)      => "第四象限",
11
};
12

13
// not 模式在 null 检查中极其常用
14
if (obj is not null)
15
    Console.WriteLine(obj.ToString());
16

17
// 等价于 old-style:
18
// if (obj != null) —— 但当 obj 重载了 != 时，is not null 是纯引用检查

1
// 游戏控制台命令解析
2
string ExecuteCommand(params string[] args) => args switch
3
{
4
    ["help"]                                       => "显示帮助",
5
    ["move", var direction]                        => $"向 {direction} 移动",
6
    ["attack", var target, var skill]              => $"用 {skill} 攻击 {target}",
7
    ["trade", "buy", var item, var count]          => $"购买 {count} 个 {item}",
8
    ["trade", "sell", var item]                    => $"出售 {item}",
9
    ["save"]                                       => "存档完成",
10
    ["load", .. var slots]                         => $"加载存档: {string.Join(", ", slots)}",
11
    []                                             => "请输入命令",
12
    _                                               => "未知命令"
13
};
14

15
// 切分模式：匹配任意长度的中间部分
16
int[] numbers = { 1, 2, 3, 4, 5 };
17
string result = numbers switch
18
{
19
    [1, .. var middle, 5] => $"中间是 [{string.Join(", ", middle)}]",  // [2, 3, 4]
20
    [1, ..]                => "以1开头",
21
    [.., 5]                => "以5结尾",
22
    _                      => "不匹配"
23
};

1
// switch 语句（C# 1-6）—— 需要 break，可以多行语句
2
string grade;
3
switch (score)
4
{
5
    case >= 90:
6
        grade = "A";
7
        break;
8
    case >= 80:
9
        grade = "B";
10
        break;
11
    case >= 70:
12
        grade = "C";
13
        break;
14
    default:
15
        grade = "F";
16
        break;
17
}
18

19
// switch 表达式（C# 8）—— 返回值的表达式，无需 break
20
string grade = score switch
21
{
22
    >= 90 => "A",
23
    >= 80 => "B",
24
    >= 70 => "C",
25
    _     => "F"
26
};

1
// C# 源码
2
object obj = "hello";
3
if (obj is string s && s.Length > 3)
4
    Console.WriteLine(s);
5

6
// 编译器生成的等效代码
7
// IL 层面：isinst string + brfalse + stloc
8
// 伪代码恢复：
9
string s;
10
if (obj is string)           // L_0006: isinst string → L_000B: brfalse
11
{
12
    s = (string)obj;         // L_0010: stloc.0
13
    if (s.Length > 3)        // L_0011: callvirt get_Length → L_0016: ldc.i4.3 → ble
14
    {
15
        Console.WriteLine(s);
16
    }
17
}

1
// 当你写 public record Character(string Name, int Level, string Job);
2
// 编译器三秒内为你生成以下所有代码：
3

4
// 1. 属性（init-only）
5
public string Name { get; init; }
6
public int Level { get; init; }
7
public string Job { get; init; }
8

9
// 2. 构造函数 + Deconstruct
10
public Character(string Name, int Level, string Job) { /* ... */ }
11
public void Deconstruct(out string Name, out int Level, out string Job) { /* ... */ }
12

13
// 3. 值相等比较
14
protected virtual Type EqualityContract => typeof(Character);
15
public override bool Equals(object obj) => obj is Character other
16
    && EqualityContract == other.EqualityContract
17
    && EqualityComparer<string>.Default.Equals(Name, other.Name)
18
    && EqualityComparer<int>.Default.Equals(Level, other.Level)
19
    && EqualityComparer<string>.Default.Equals(Job, other.Job);
20

21
public override int GetHashCode() => HashCode.Combine(Name, Level, Job);
22

23
// 4. ToString
24
public override string ToString() => $"Character {{ Name = {Name}, Level = {Level}, Job = {Job} }}";
25

26
// 5. <Clone>$ 方法（供 with 表达式调用）
27
public virtual Character <Clone>$() => new Character(this);
28
protected Character(Character original) { Name = original.Name; ... }

1
// 你的源码中标注 [AutoToString]
2
[AttributeUsage(AttributeTargets.Class)]
3
public class AutoToStringAttribute : Attribute { }
4

5
// Source Generator 在编译时生成：
6
[Generator]
7
public class AutoToStringGenerator : ISourceGenerator
8
{
9
    public void Initialize(GeneratorInitializationContext context)
10
    {
11
        // 注册语法接收器
12
        context.RegisterForSyntaxNotifications(() => new AttributeSyntaxReceiver());
13
    }
14

15
    public void Execute(GeneratorExecutionContext context)
16
    {
17
        // 对每个标记了 [AutoToString] 的类，生成 ToString() 重写
18
        foreach (var classSymbol in GetMarkedClasses(context))
19
        {
20
            var source = GenerateToString(classSymbol);
21
            context.AddSource($"{classSymbol.Name}.ToString.g.cs", source);
22
        }
23
    }
24
}

1
// C# 12 之前
2
public class GameTimer
3
{
4
    private readonly float _duration;
5
    private readonly Action _onComplete;
6
    private float _elapsed;
7

8
    public GameTimer(float duration, Action onComplete)
9
    {
10
        _duration = duration;
11
        _onComplete = onComplete;
12
        _elapsed = 0;
13
    }
14
}
15

16
// C# 12：Primary Constructor（class 版）
17
public class GameTimer(float duration, Action onComplete)
18
{
19
    private float _elapsed;
20

21
    public void Tick(float delta)
22
    {
23
        _elapsed += delta;
24
        if (_elapsed >= duration)
25
            onComplete();
26
            // duration 和 onComplete 在整个类体内可用
27
    }
28
}

1
// 编译警告：switch 表达式未处理所有输入
2
string GetName(int id) => id switch
3
{
4
    1 => "One",
5
    2 => "Two",
6
    // 缺少 _ 丢弃模式！
7
};
8

9
// 正确：始终加 _ 或穷举所有可能值
10
string GetName(int id) => id switch
11
{
12
    1 => "One",
13
    2 => "Two",
14
    _ => "Unknown"
15
};
16

17
// 但 bool/enum 等有限类型，编译器能做穷举检查
18
// 如果 enum 只有 A, B, C 三个值，switch 表达式覆盖了 A, B, C 就不需要 _

1
// 定义技能效果
2
public abstract record SkillEffect;
3
public record DamageEffect(float Amount, ElementType Element) : SkillEffect;
4
public record HealEffect(float Amount, bool CanRevive) : SkillEffect;
5
public record StatusEffect(StatusType Type, float Duration, float Chance) : SkillEffect;
6
public record CompositeEffect(SkillEffect First, SkillEffect Second) : SkillEffect;
7

8
// 处理效果 —— 模式匹配让逻辑清晰无比
9
void ApplyEffect(SkillEffect effect, CharacterStats target)
10
{
11
    switch (effect)
12
    {
13
        case DamageEffect { Amount: >= 1000, Element: ElementType.Fire }:
14
            // 大伤害火焰特殊处理
15
            target.TakeDamage(1000, isCritical: true);
16
            SpawnFireParticles(target.Position);
17
            break;
18

19
        case DamageEffect { Amount: var dmg, Element: var elem }:
20
            var multiplier = target.GetResistance(elem);
21
            target.TakeDamage(dmg * multiplier);
22
            break;
23

24
        case HealEffect { CanRevive: true } when target.IsDead:
25
            // 复活逻辑
26
            target.Revive(effect.Amount * 0.5f);  // 复活只恢复一半
27
            break;
28

29
        case HealEffect { Amount: var heal }:
30
            target.Heal(heal);
31
            break;
32

33
        case StatusEffect { Chance: var c, Duration: > 10f }:
34
            // 长时间的 DEBUFF 有特殊播放提示
35
            if (Random.value < c)
36
                target.ApplyStatus(effect.Type, effect.Duration, showWarning: true);
37
            break;
38

39
        case StatusEffect s:
40
            if (Random.value < s.Chance)
41
                target.ApplyStatus(s.Type, s.Duration);
42
            break;
43

44
        case CompositeEffect { First: var f, Second: var s }:
45
            ApplyEffect(f, target);  // 递归处理组合效果
46
            ApplyEffect(s, target);
47
            break;
48

49
        default:
50
            Debug.LogWarning($"未处理的技能效果类型: {effect.GetType()}");
51
            break;
52
    }
53
}

1
public readonly record struct GameConfig
2
(
3
    int Width,
4
    int Height,
5
    int TargetFPS,
6
    float MasterVolume,
7
    bool EnableDebug
8
)
9
{
10
    // 预设配置
11
    public static readonly GameConfig Default = new(1920, 1080, 60, 1.0f, false);
12
    public static readonly GameConfig MobileLow = Default with
13
    {
14
        Width = 1280,
15
        Height = 720,
16
        TargetFPS = 30,
17
        EnableDebug = false
18
    };
19
    public static readonly GameConfig EditorDebug = Default with { EnableDebug = true };
20
}
21

22
// 运行时按需派生
23
var current = GameConfig.Default;
24
if (Application.isMobilePlatform)
25
    current = current with { Width = Screen.width, Height = Screen.height };
26
if (QualitySettings.GetQualityLevel() < 3)
27
    current = current with { TargetFPS = 30 };

1
// 假设服务器发来的消息格式: 命令名 + 变长参数
2
string RouteMessage(string[] tokens) => tokens switch
3
{
4
    ["PING"]                                              => HandlePing(),
5
    ["JOIN", var roomId]                                 => HandleJoin(roomId),
6
    ["CHAT", var channel, .. var msgParts]               => HandleChat(channel, string.Join(" ", msgParts)),
7
    ["MOVE", var x, var y, var z]                        => HandleMove(float.Parse(x), float.Parse(y), float.Parse(z)),
8
    ["ATTACK", var targetId, var skillId, var param]     => HandleAttack(targetId, skillId, param),
9
    ["SYSTEM", "KICK", var playerId, var reason]         => HandleKick(playerId, reason),
10
    ["SYSTEM", "BAN", var playerId, .. var banArgs]      => HandleBan(playerId, banArgs),
11
    ["SYSTEM", ..]                                        => "未知系统命令",
12
    ["ERROR", var code]                                   => HandleError(int.Parse(code)),
13
    [] or [" "]                                           => "空消息",
14
    _                                                     => $"未识别的消息: {string.Join(" ", tokens)}"
15
};