iOS反射

id obj = [[NSMutableArray alloc] init];

// 类型判断
[obj isKindOfClass:[NSArray class]];           // YES — 判断是否是某个类或其子类的实例
[obj isMemberOfClass:[NSMutableArray class]];  // YES — 判断是否是某个类的直接实例
[obj conformsToProtocol:@protocol(NSCoding)];  // YES — 判断是否遵循某个协议

// 方法响应检查
[obj respondsToSelector:@selector(addObject:)]; // YES — 判断是否能响应某个消息

// 获取类型信息
NSStringFromClass([obj class]);          // @"__NSArrayM"（真实的私有子类名）
NSStringFromSelector(@selector(count));  // @"count"

#import <objc/runtime.h>

Class cls = [MyClass class];

// 获取类名和继承关系
const char *name = class_getName(cls);           // "MyClass"
Class superCls = class_getSuperclass(cls);       // 父类
BOOL isMeta = class_isMetaClass(cls);            // 是否是元类
size_t size = class_getInstanceSize(cls);        // 实例大小（字节）

// 获取属性列表
unsigned int propCount;
objc_property_t *props = class_copyPropertyList(cls, &propCount);
for (unsigned int i = 0; i < propCount; i++) {
    const char *propName = property_getName(props[i]);
    const char *propAttrs = property_getAttributes(props[i]);
    NSLog(@"属性: %s, 特性: %s", propName, propAttrs);
}
free(props);

// 获取成员变量列表
unsigned int ivarCount;
Ivar *ivars = class_copyIvarList(cls, &ivarCount);
for (unsigned int i = 0; i < ivarCount; i++) {
    const char *ivarName = ivar_getName(ivars[i]);
    const char *ivarType = ivar_getTypeEncoding(ivars[i]);
    ptrdiff_t offset = ivar_getOffset(ivars[i]);
    NSLog(@"成员变量: %s, 类型编码: %s, 偏移量: %td", ivarName, ivarType, offset);
}
free(ivars);

// 获取方法列表
unsigned int methodCount;
Method *methods = class_copyMethodList(cls, &methodCount);
for (unsigned int i = 0; i < methodCount; i++) {
    SEL sel = method_getName(methods[i]);
    const char *typeEncoding = method_getTypeEncoding(methods[i]);
    NSLog(@"方法: %@, 类型编码: %s", NSStringFromSelector(sel), typeEncoding);
}
free(methods);

// 获取协议列表
unsigned int protocolCount;
Protocol * __unsafe_unretained *protocols = class_copyProtocolList(cls, &protocolCount);
for (unsigned int i = 0; i < protocolCount; i++) {
    NSLog(@"协议: %s", protocol_getName(protocols[i]));
}
free(protocols);

// 创建 NSObject 的子类 "DynamicPerson"
Class PersonClass = objc_allocateClassPair([NSObject class], "DynamicPerson", 0);

// 添加成员变量（必须在 objc_registerClassPair 之前）
class_addIvar(PersonClass, "_name", sizeof(NSString *), log2(sizeof(NSString *)), @encode(NSString *));
class_addIvar(PersonClass, "_age", sizeof(int), log2(sizeof(int)), @encode(int));

// 添加方法
class_addMethod(PersonClass, @selector(description), (IMP)personDescription, "@@:");

// 注册类（注册后不能再添加成员变量）
objc_registerClassPair(PersonClass);

// 使用
id person = [[PersonClass alloc] init];
[person setValue:@"Tom" forKey:@"name"];
NSLog(@"%@", person);  // 调用 personDescription

NSString *personDescription(id self, SEL _cmd) {
    Ivar nameIvar = class_getInstanceVariable([self class], "_name");
    NSString *name = object_getIvar(self, nameIvar);
    return [NSString stringWithFormat:@"DynamicPerson: %@", name];
}

// 添加方法
class_addMethod([MyClass class], @selector(newMethod), (IMP)newMethodIMP, "v@:");

// 替换方法实现
class_replaceMethod([MyClass class], @selector(existingMethod), (IMP)newIMP, "v@:");

// 交换两个方法的实现
Method m1 = class_getInstanceMethod([MyClass class], @selector(method1));
Method m2 = class_getInstanceMethod([MyClass class], @selector(method2));
method_exchangeImplementations(m1, m2);

// 获取和设置方法实现
IMP oldIMP = method_getImplementation(m1);
method_setImplementation(m1, (IMP)customIMP);

// 字符串 → 类
Class cls = NSClassFromString(@"UIViewController");
id vc = [[cls alloc] init];

// 字符串 → SEL
SEL sel = NSSelectorFromString(@"viewDidLoad");
if ([vc respondsToSelector:sel]) {
    [vc performSelector:sel];
}

// 反向转换
NSString *className = NSStringFromClass([vc class]);   // @"UIViewController"
NSString *selName = NSStringFromSelector(sel);         // @"viewDidLoad"

struct Person {
    let name: String
    var age: Int
    private var secret: String = "hidden"
}

let person = Person(name: "Tom", age: 25)
let mirror = Mirror(reflecting: person)

// 获取类型信息
print(mirror.subjectType)        // Person
print(mirror.displayStyle)       // Optional(.struct)

// 遍历所有存储属性（包括 private）
for child in mirror.children {
    print("\(child.label ?? "nil"): \(child.value)")
}
// 输出：
// name: Tom
// age: 25
// secret: hidden

for child in mirror.children {
    let label = child.label   // 属性名（可选，元组元素可能没有名字）
    let value = child.value   // 属性值（Any 类型）
    let valueMirror = Mirror(reflecting: value)
    print("属性: \(label ?? "?"), 值: \(value), 类型: \(valueMirror.subjectType)")
}

class Animal {
    var species: String = "Unknown"
}

class Dog: Animal {
    var name: String = "Buddy"
    var breed: String = "Labrador"
}

let dog = Dog()
var currentMirror: Mirror? = Mirror(reflecting: dog)

while let mirror = currentMirror {
    print("--- \(mirror.subjectType) ---")
    for child in mirror.children {
        print("  \(child.label ?? "?"): \(child.value)")
    }
    currentMirror = mirror.superclassMirror
}
// 输出：
// --- Dog ---
//   name: Buddy
//   breed: Labrador
// --- Animal ---
//   species: Unknown

enum NetworkError {
    case timeout
    case serverError(code: Int, message: String)
    case noConnection
}

let error = NetworkError.serverError(code: 500, message: "Internal Server Error")
let mirror = Mirror(reflecting: error)

print(mirror.displayStyle)       // Optional(.enum)

for child in mirror.children {
    print("case: \(child.label ?? "?"), 关联值: \(child.value)")
}
// 输出：
// case: serverError, 关联值: (code: 500, message: "Internal Server Error")

Mirror(reflecting: value)
        │
        ▼
获取 value 的类型元数据（Type Metadata）
        │
        ▼
查找 Type Descriptor → Field Descriptor
        │
        ▼
遍历 Field Descriptor 中的字段记录
        │
        ├── 读取字段名称（从 __swift5_reflstr）
        ├── 计算字段偏移量（从元数据中的 Field Offset Vector）
        └── 读取字段值（从 value 内存 + 偏移量）
        │
        ▼
构建 Mirror.Child 数组

struct Credentials: CustomReflectable {
    let username: String
    let password: String
    
    var customMirror: Mirror {
        Mirror(self, children: [
            "username": username,
            "password": String(repeating: "*", count: password.count)
        ])
    }
}

let creds = Credentials(username: "admin", password: "secret123")
let mirror = Mirror(reflecting: creds)
for child in mirror.children {
    print("\(child.label ?? "?"): \(child.value)")
}
// 输出：
// username: admin
// password: *********

func dump<T>(_ value: T, indent: Int = 0) -> String {
    let mirror = Mirror(reflecting: value)
    let prefix = String(repeating: "  ", count: indent)
    
    if mirror.children.isEmpty {
        return "\(value)"
    }
    
    var lines = ["\(mirror.subjectType) {"]
    for child in mirror.children {
        let childDesc = dump(child.value, indent: indent + 1)
        lines.append("\(prefix)  \(child.label ?? "?"): \(childDesc)")
    }
    lines.append("\(prefix)}")
    return lines.joined(separator: "\n")
}

func toJSON<T>(_ value: T) -> Any {
    let mirror = Mirror(reflecting: value)
    
    if mirror.children.isEmpty {
        return value
    }
    
    if mirror.displayStyle == .collection {
        return mirror.children.map { toJSON($0.value) }
    }
    
    if mirror.displayStyle == .dictionary {
        var dict: [String: Any] = [:]
        for child in mirror.children {
            if let pair = child.value as? (key: AnyHashable, value: Any) {
                dict["\(pair.key)"] = toJSON(pair.value)
            }
        }
        return dict
    }
    
    var dict: [String: Any] = [:]
    for child in mirror.children {
        guard let label = child.label else { continue }
        let childMirror = Mirror(reflecting: child.value)
        if childMirror.displayStyle == .optional {
            if let firstChild = childMirror.children.first {
                dict[label] = toJSON(firstChild.value)
            }
        } else {
            dict[label] = toJSON(child.value)
        }
    }
    return dict
}

+ (instancetype)modelWithDict:(NSDictionary *)dict {
    id obj = [[self alloc] init];
    
    unsigned int count;
    objc_property_t *props = class_copyPropertyList(self, &count);
    
    for (unsigned int i = 0; i < count; i++) {
        NSString *propName = [NSString stringWithUTF8String:property_getName(props[i])];
        id value = dict[propName];
        if (value && value != [NSNull null]) {
            [obj setValue:value forKey:propName];
        }
    }
    
    free(props);
    return obj;
}

- (UIViewController *)viewControllerForURL:(NSURL *)url {
    NSString *path = url.path;  // 例如 "/user/profile"
    
    // 路由表：URL path → 类名
    NSDictionary *routeMap = @{
        @"/user/profile": @"UserProfileViewController",
        @"/order/detail": @"OrderDetailViewController",
    };
    
    NSString *className = routeMap[path];
    if (!className) return nil;
    
    Class cls = NSClassFromString(className);
    if (!cls) return nil;
    
    UIViewController *vc = [[cls alloc] init];
    
    // 通过 URL 参数自动设置属性
    NSDictionary *params = [self parseQueryParams:url];
    for (NSString *key in params) {
        // 构造 setter 名称：key "userId" → "setUserId:"
        NSString *setterName = [NSString stringWithFormat:@"set%@%@:",
            [[key substringToIndex:1] uppercaseString],
            [key substringFromIndex:1]];
        if ([vc respondsToSelector:NSSelectorFromString(setterName)]) {
            [vc setValue:params[key] forKey:key];
        }
    }
    
    return vc;
}

func assertEqual<T>(_ actual: T, _ expected: T, file: StaticString = #file, line: UInt = #line) {
    let actualMirror = Mirror(reflecting: actual)
    let expectedMirror = Mirror(reflecting: expected)
    
    for (actualChild, expectedChild) in zip(actualMirror.children, expectedMirror.children) {
        let actualStr = String(describing: actualChild.value)
        let expectedStr = String(describing: expectedChild.value)
        if actualStr != expectedStr {
            print("属性 \(actualChild.label ?? "?") 不匹配: 实际=\(actualStr), 期望=\(expectedStr)")
        }
    }
}

class MyObject: NSObject {
    @objc var name: String = "Tom"
    var age: Int = 25    // 非 @objc 属性
}

let obj = MyObject()

// Swift Mirror：能看到所有存储属性
let mirror = Mirror(reflecting: obj)
for child in mirror.children {
    print("\(child.label ?? "?"): \(child.value)")
}
// name: Tom
// age: 25

// OC Runtime：只能看到 @objc 属性
var count: UInt32 = 0
let properties = class_copyPropertyList(type(of: obj), &count)
for i in 0..<Int(count) {
    let name = String(cString: property_getName(properties![i]))
    print("OC property: \(name)")
}
free(properties)
// OC property: name（age 不会出现，因为没有 @objc 标记）