Swift进阶教程Mirror反射示例详解

目录

• 元类型与.self
• AnyObject
• AnyClass
• Any
• type(Of:)
• self
• self在方法里面的作用
• Self
• Swift Runtime
• Mirror
• Mirror的基本用法
• Mirror的简单应用-JSON解析
• Mirror源码解析
• Enum Metadata探索
• 还原TargetEnumMetadata
• 还原TargetEnumDescriptor
• 相对偏移指针
• 打印枚举中的属性
• Struct Metadata探索
• 获取结构体的属性
• swift_getTypeByMangledNameInContext 函数
• 获取属性的值

class LGTeacher {
    var age = 18
}
var t = LGTeacher()
var t1: AnyObject = t //代表LGTeacher类的实例
var t2: AnyObject = LGTeacher.self //代表LGTeacher类的类型

public typealias AnyClass = AnyObject.Type

var array:[AnyObject] = [1,2]

var array:[Any] = [1,2]

class LGTeacher {
    var age:Int = 18
    func teach() {
        print("teach")
    }
}
//⾸先通过构造⽅法构建⼀个Mirror实例，这⾥传⼊的参数是 Any，也就意味着当前可以是类，结构体，枚举等
let mirror = Mirror(reflecting: LGTeacher())
//接下来遍历 children 属性，这是⼀个集合
for pro in mirror.children {
    //然后我们可以直接通过 label 输出当前的名称，value 输出当前反射的值
    print("(pro.label) : (pro.value)")
}

class LGTeacher {
    var age:Int = 18
    var name = "FY"
}
enum JSONMapError: Error {
    case emptyKey
    case notConformProtocol
}
protocol JSONMap {
    func jsonMap() -> Any
}
extension JSONMap {
    func jsonMap() -> Any {
        let mirror = Mirror(reflecting: self)
        guard !mirror.children.isEmpty else {
            return self
        }
     
        var result: [String: Any] = [:]
      
        for child in mirror.children {
            if let value = child.value as? JSONMap {
                if let key = child.label {
                    result[key] = try? value.jsonMap()
                }
            } else {
                return JSONMapError.notConformProtocol
            }
        }        
        return result
    }
}
extension LGTeacher: JSONMap{}
extension Int: JSONMap{}
extension String: JSONMap{}
print(LGTeacher().jsonMap())
//
["age": 18, "name": "FY"]

public init(reflecting subject: Any) {
    if case let customized as CustomReflectable = subject {
        self = customized.customMirror
    } else {
        self = Mirror(internalReflecting: subject)
    }
}

static std::pair<StringRef /*name*/, FieldType /*fieldInfo*/>
getFieldAt(const Metadata *base, unsigned index) {
    using namespace reflection;
    auto failedToFindMetadata = [&]() -> std::pair<StringRef, FieldType> {
        auto typeName = swift_getTypeName(base, /*qualified*/ true);
        missing_reflection_metadata_warning(
            "warning: the Swift runtime found no field metadata for "
            "type "%*s" that claims to be reflectable. Its fields will show up as "
            ""unknown" in Mirrors
",
            (int)typeName.length, typeName.data);
        return {"unknown", FieldType(&METADATA_SYM(EMPTY_TUPLE_MANGLING))};
    };
    auto *baseDesc = base->getTypeContextDescriptor();
    if (!baseDesc) return failedToFindMetadata();
    auto *fields = baseDesc->Fields.get();
    if (!fields) return failedToFindMetadata();
    auto &field = fields->getFields()[index];
// Bounds are always valid as the offset is constant.
    auto name = field.getFieldName();
// Enum cases don"t always have types.
    if (!field.hasMangledTypeName())
        return {name, FieldType::untypedEnumCase(field.isIndirectCase())};
    auto typeName = field.getMangledTypeName();
    SubstGenericParametersFromMetadata substitutions(base);
    auto result = swift_getTypeByMangledName(
        MetadataState::Complete, typeName, substitutions.getGenericArgs(),
        [&substitutions](unsigned depth, unsigned index) {
            return substitutions.getMetadata(depth, index);
        },
        [&substitutions](const Metadata *type, unsigned index) {
        return substitutions.getWitnessTable(type, index);
    });
// If demangling the type failed, pretend it"s an empty type instead with
// a log message.
    TypeInfo typeInfo;
    if (result.isError()) {
        typeInfo = TypeInfo({&METADATA_SYM(EMPTY_TUPLE_MANGLING),
        MetadataState::Complete}, {});
        auto *error = result.getError();
        char *str = error->copyErrorString();
        missing_reflection_metadata_warning(
            "warning: the Swift runtime was unable to demangle the type "
            "of field "%*s". the mangled type name is "%*s": %s. this field will "
            "show up as an empty tuple in Mirrors
",
            (int)name.size(), name.data(), (int)typeName.size(), typeName.data(),
            str);
        error->freeErrorString(str);
    } else {
        typeInfo = result.getType();
    }
    auto fieldType = FieldType(typeInfo.getMetadata());
    fieldType.setIndirect(field.isIndirectCase());
    fieldType.setReferenceOwnership(typeInfo.getReferenceOwnership());
    fieldType.setIsVar(field.isVar());
    return {name, fieldType};

struct TargetEnumMetadata : public TargetValueMetadata<Runtime> {
}
struct TargetValueMetadata : public TargetMetadata<Runtime> {
    TargetSignedPointer<Runtime, const TargetValueTypeDescriptor<Runtime> *Description;
}
struct TargetMetadata {
    StoredPointer Kind;
}

struct TargetEnumMetadata {
    var kind: Int
    var typeDescriptor: UnsafeRawPointer
}

const TargetEnumDescriptor<Runtime> *getDescription() const {
    return llvm::cast<TargetEnumDescriptor<Runtime>>(this->Description);
}

class TargetEnumDescriptor final : public TargetValueTypeDescriptor<Runtime>,
        public TrailingGenericContextObjects<TargetEnumDescriptor<Runtime>,
        TargetTypeGenericContextDescriptorHeader,
/*additional trailing objects*/
        TargetForeignMetadataInitialization<Runtime>,
        TargetSingletonMetadataInitialization<Runtime>,
        TargetCanonicalSpecializedMetadatasListCount<Runtime>,
        TargetCanonicalSpecializedMetadatasListEntry<Runtime>,
        TargetCanonicalSpecializedMetadatasCachingOnceToken<Runtime>> {
    uint32_t NumPayloadCasesAndPayloadSizeOffset;
    uint32_t NumEmptyCases;
}
class TargetValueTypeDescriptor: public TargetTypeContextDescriptor<Runtime> {
}
class TargetTypeContextDescriptor: public TargetContextDescriptor<Runtime> {
    TargetRelativeDirectPointer<Runtime, const char, /*nullable*/ false> Name;
    TargetRelativeDirectPointer<Runtime, MetadataResponse(...), /*Nullable*/ true> AccessFunctionPtr;
    TargetRelativeDirectPointer<Runtime, const reflection::FieldDescriptor,/*nullable*/ true> Fields;
}
struct TargetContextDescriptor {
    ContextDescriptorFlags Flags;
    TargetRelativeContextPointer<Runtime> Parent;
}

struct TargetEnumDescriptor{
    var flags: Int32
    var parent: TargetRelativeDirectPointer<UnsafeRawPointer>
    var name: TargetRelativeDirectPointer<CChar>
    var accessFunctionPointer: TargetRelativeDirectPointer<UnsafeRawPointer>
    var fieldDescriptor: TargetRelativeDirectPointer<UnsafeRawPointer>
    var NumPayloadCasesAndPayloadSizeOffset: UInt32
    var NumEmptyCases: UInt32
}

struct TargetEnumMetadata{
    var kind: Int
    var typeDescriptor: UnsafeMutablePointer<TargetEnumDescriptor>
}

struct TargetRelativeDirectPointer<Pointee>{
    var offset: Int32
    
    mutating func getmeasureRelativeOffset() -> UnsafeMutablePointer<Pointee>{
        let offset = **self**.offset   
        return withUnsafePointer(to: &self) { p in
           return UnsafeMutablePointer(mutating: UnsafeRawPointer(p).advanced(by: numericCast(offset)).assumingMemoryBound(to: Pointee.self))
        }
    }
}

enum Planet {
    case mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
}
let ptr = unsafeBitCast(Planet.self as Any.Type to:UnsafeMutablePointer<TargetEnumMetadata>.self)
let namePtr = ptr.pointee.typeDescriptor.pointee.name.getmeasureRelativeOffset()
print("name: ",String(cString: namePtr))
print("NumPayloadCasesAndPayloadSizeOffset ",ptr.pointee.typeDescriptor.pointee.NumPayloadCasesAndPayloadSizeOffset)
print("NumEmptyCases ",ptr.pointee.typeDescriptor.pointee.NumEmptyCases)

name:  Planet
NumPayloadCasesAndPayloadSizeOffset  0
NumEmptyCases  8

struct TargetStructMetadata {
    var kind: Int
    var typeDescriptor: UnsafeRawPointer
}

class TargetStructDescriptor final: public TargetValueTypeDescriptor<Runtime>,
        public TrailingGenericContextObjects<TargetStructDescriptor<Runtime>,
                TargetTypeGenericContextDescriptorHeader,
/*additional trailing objects*/
                TargetForeignMetadataInitialization<Runtime>,
                TargetSingletonMetadataInitialization<Runtime>,
                TargetCanonicalSpecializedMetadatasListCount<Runtime>,
                TargetCanonicalSpecializedMetadatasListEntry<Runtime>,
                TargetCanonicalSpecializedMetadatasCachingOnceToken<Runtime>> {
    uint32_t NumFields;
    uint32_t FieldOffsetVectorOffset;
}

struct TargetStructDescriptor{
    var flags: Int32
    var parent: TargetRelativeDirectPointer<UnsafeRawPointer>
    var name: TargetRelativeDirectPointer<CChar>
    var accessFunctionPointer: TargetRelativeDirectPointer<UnsafeRawPointer>
    var fieldDescriptor: TargetRelativeDirectPointer<FieldDescriptor>
    var NumFields: UInt32
    var FieldOffsetVectorOffset: UInt32
    ```
    func getFieldOffsets(_ metadata: UnsafeRawPointer) -> UnsafePointer<Int32> {
            return UnsafeRawPointer(metadata.assumingMemoryBound(to: Int.self).advanced(by: numericCast(self.FieldOffsetVectorOffset))).assumingMemoryBound(to: Int32.self)
    }
    //参考handyjson 中
    var genericArgumentOffset: Int {
        return 2
    }

此时`TargetStructMetadata`中的数据结构也可以修改一下
```swift
struct TargetStructMetadata{
    var kind: Int
    var typeDescriptor: UnsafeMutablePointer<TargetStructDescriptor>
}

class FieldDescriptor {
    const FieldRecord *getFieldRecordBuffer() const {
        return reinterpret_cast<const FieldRecord *>(this + 1);
    }
public:
    const RelativeDirectPointer<const char> MangledTypeName;
    const RelativeDirectPointer<const char> Superclass;
    FieldDescriptor() = delete;
    const FieldDescriptorKind Kind;
    const uint16_t FieldRecordSize;
    const uint32_t NumFields;
    llvm::ArrayRef<FieldRecord> getFields() const {
        return {getFieldRecordBuffer(), NumFields};
    }
}

struct FieldDescriptor {
    var MangledTypeName: TargetRelativeDirectPointer<CChar>
    var Superclass: TargetRelativeDirectPointer<CChar>
    var Kind: UInt16
    var FieldRecordSize:UInt16
    var NumFields: UInt32
    var fields: FieldRecordBuffer<FieldRecord>
}

struct FiledRecordBuffer<Element>{
    var element: Element    
    mutating func buffer(n: Int) -> UnsafeBufferPointer<Element> {
        return withUnsafePointer(to: &self) {
            let ptr = $0.withMemoryRebound(to: Element.self, capacity: 1) { start in
                return start
            }
            return UnsafeBufferPointer(start: ptr, count: n)
        }
    }
    
    mutating func index(of i: Int) -> UnsafeMutablePointer<Element> {
        return withUnsafePointer(to: &self) {
            return UnsafeMutablePointer(mutating: UnsafeRawPointer($0).assumingMemoryBound(to: Element.self).advanced(by: i))
        }
    }
}

class FieldRecord {
    const FieldRecordFlags Flags;
public:
    const RelativeDirectPointer<const char> MangledTypeName;
    const RelativeDirectPointer<const char> FieldName;
}

struct FieldRecord {
    var Flags: UInt32
    var MangledTypeName: TargetRelativeDirectPointer<CChar>
    var FieldName: TargetRelativeDirectPointer<CChar>
}

@_silgen_name("swift_getTypeByMangledNameInContext")
func swift_H_getTypeByMangledNameInContext(typeName: UnsafeRawPointer, len: Int, context: UnsafeRawPointer, generic: UnsafeRawPointer) -> UnsafeRawPointer
protocol BridgeProtocol {
}
extension BridgeProtocol {
    static func get(from pointer: UnsafeRawPointer) -> Any {
        pointer.assumingMemoryBound(to: Self.self).pointee
    }
}
struct BridgeProtocolMetadata {
    let type: Any.Type
    let witness: Int
}
func customCast(type: Any.Type) -> BridgeProtocol.Type {
    let container = BridgeProtocolMetadata(type: type, witness: 0)
    let cast = unsafeBitCast(container, to: BridgeProtocol.Type.self)
    return cast
}
struct LGStudent {
    var age = 18
    var name = "FWJ"
    let money = 2000
}
var t = LGStudent()
let ptr = unsafeBitCast(LGStudent.self as Any.Type, to: UnsafeMutablePointer<TargetStructMetadata>.self)
print("----------开始解析---------------")
let namePtr = ptr.pointee.typeDescriptor.pointee.name.getmeasureRelativeOffset()
let filedNum = ptr.pointee.typeDescriptor.pointee.NumFields
print("当前结构体的名称: (String(cString: namePtr))")
print("当前结构体的属性数量 (filedNum)")
print("============开始解析属性============")
let offsets = ptr.pointee.typeDescriptor.pointee.getFieldOffsets(UnsafeRawPointer(ptr).assumingMemoryBound(to: Int.self))
for i in 0..<filedNum {
    let fieldRecord = ptr.pointee.typeDescriptor.pointee.fieldDescriptor.getmeasureRelativeOffset().pointee.fields.index(of: Int(i))
   
    let fieldOffset = offsets[Int(i)]
    let fieldName = fieldRecord.pointee.FieldName.getmeasureRelativeOffset()
    print("--- (String(cString: fieldName)) 属性信息 ---")    
    let mangledTypeName = fieldRecord.pointee.MangledTypeName.getmeasureRelativeOffset()
    print("mangledTypeName: (String(cString: mangledTypeName))")
    
    let typeNameLength = Int(256)    
    let genericVector = UnsafeRawPointer(ptr).advanced(by: ptr.pointee.typeDescriptor.pointee.genericArgumentOffset * MemoryLayout<UnsafeRawPointer>.size).assumingMemoryBound(to: Any.Type.self)
    
    **let** fieldType = swift_H_getTypeByMangledNameInContext(typeName: mangledTypeName, len: typeNameLength, context: UnsafeRawPointer(ptr.pointee.typeDescriptor), generic: genericVector)
    let type = unsafeBitCast(fieldType, to: Any.Type.self)
    print("fieldType: (type)")    
    let brigeProtocolType = customCast(type: type)
    
    let instanceAddress = withUnsafePointer(to: &t) {
        return UnsafeRawPointer($0)
    }
       
    let fieldValue = brigeProtocolType.get(from: instanceAddress.advanced(by: Int(fieldOffset)))
    print("fieldValue: (fieldValue)")
    print("--- (String(cString: fieldName)) 属性信息 ---")
}
//打印结果
----------开始解析---------------
当前结构体的名称: LGStudent**
当前结构体的属性数量 3
============开始解析属性============
--- age 属性信息 ---
mangledTypeName: Si
fieldType: Int
fieldValue: 18
--- age 属性信息 ---
--- name 属性信息 ---
mangledTypeName: SS
fieldType: String
fieldValue: FWJ
--- name 属性信息 ---
--- money 属性信息 ---
mangledTypeName: Si
fieldType: Int
fieldValue: 2000
--- money 属性信息 ---

SWIFT_CC(swift) SWIFT_RUNTIME_EXPORT
const Metadata * _Nullable
swift_getTypeByMangledNameInContext(
                             const char *typeNameStart,
                             size_t typeNameLength,
                             const TargetContextDescriptor<InProcess> *context,
                             const void * const *genericArgs) {
    llvm::StringRef typeName(typeNameStart, typeNameLength);
    SubstGenericParametersFromMetadata substitutions(context, genericArgs);
    return swift_getTypeByMangledName(MetadataState::Complete, typeName,
                                genericArgs,
                                [&substitutions](unsigned depth, unsigned index) {
                                    return substitutions.getMetadata(depth, index);
                                },
                                [&substitutions](const Metadata *type, unsigned index) {
                                    return substitutions.getWitnessTable(type, index);
                                }).getType().getMetadata();
}

@_silgen_name("swift_getTypeByMangledNameInContext")
func swift_H_getTypeByMangledNameInContext(typeName: UnsafeRawPointer, len: Int, context: UnsafeRawPointer, generic: UnsafeRawPointer) -> UnsafeRawPointer

protocol BridgeProtocol {
}
extension BridgeProtocol {
    static func get(from pointer: UnsafeRawPointer) -> Any {
        pointer.assumingMemoryBound(to: Self.self).pointee
    }
}
struct BridgeProtocolMetadata {
    let type: Any.Type
    let witness: Int
}
func customCast(type: Any.Type) -> BridgeProtocol.Type {
    let container = BridgeProtocolMetadata(type: type, witness: 0)
    let cast = unsafeBitCast(container, to: BridgeProtocol.Type.self)
    return cast
}