swift class的虚函数表、扩展、@objc修饰、虚函数的派发方式研究

swift class的虚函数表、扩展、@objc修饰的研究

工具：

swiftc -emit-sil BaseClass.swift | xcrun swift-demangle > ClassFunc.silgen

cat ClassFunc.silgen

目标：

1、@objc和@objc dynamic修饰的函数是否进入虚函数表；

2、虚函数的的派发机制是什么？函数的调用在编译器层面最终转化为apply调用；

3、extension中的缺省修饰函数是否进入虚函数表；

4、extension中的@objc修饰函数的行为；

5、结构体是否允许@objc修饰：

@objc can only be used with members of classes, @objc protocols, and concrete extensions of classes

https://www.cnblogs.com/feng9exe/p/9460336.html

class NSObjectBase: NSObject {

func Msg_Normal(){ print("Msg_Normal") }

func Msg_Second(){ print("Msg_Second") }

func Msg_Third(){ print("Msg_Second") }

@objc func Msg_ObjcX(){}

@objc dynamic func Msg_Objc_Dynamic(){}

func callTest(){self.Msg_Normal()}

func callAgain(){self.Msg_Third()}

}

extension NSObjectBase{

@objc func OcExtensionFunc(){print("OcExtensionFunc")}

}

class DerivedOcClass:NSObjectBase{

override func OcExtensionFunc(){print("DerivedOcClass OcExtensionFunc")}

}

// NSObjectBase.Msg_Objc_DynamicX()

sil hidden @NSObjectBase.NSObjectBase.Msg_Objc_DynamicX() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () {

// %0                                             // user: %1

bb0(%0 : $NSObjectBase):

debug_value %0 : $NSObjectBase, let, name "self", argno 1 // id: %1

%2 = tuple ()                                   // user: %3

return %2 : $()                                 // id: %3

} // end sil function 'NSObjectBase.NSObjectBase.Msg_Objc_DynamicX() -> ()'

// @objc NSObjectBase.Msg_Objc_DynamicX()

sil hidden [thunk] @@objc NSObjectBase.NSObjectBase.Msg_Objc_DynamicX() -> () : $@convention(objc_method) (NSObjectBase) -> () {

// %0                                             // users: %4, %3, %1

bb0(%0 : $NSObjectBase):

strong_retain %0 : $NSObjectBase                // id: %1

// function_ref NSObjectBase.Msg_Objc_DynamicX()

%2 = function_ref @NSObjectBase.NSObjectBase.Msg_Objc_DynamicX() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () // user: %3

%3 = apply %2(%0) : $@convention(method) (@guaranteed NSObjectBase) -> () // user: %5

strong_release %0 : $NSObjectBase               // id: %4

return %3 : $()                                 // id: %5

} // end sil function '@objc NSObjectBase.NSObjectBase.Msg_Objc_DynamicX() -> ()'

// NSObjectBase.Msg_ObjcX()

sil hidden @NSObjectBase.NSObjectBase.Msg_ObjcX() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () {

// %0                                             // user: %1

bb0(%0 : $NSObjectBase):

debug_value %0 : $NSObjectBase, let, name "self", argno 1 // id: %1

%2 = tuple ()                                   // user: %3

return %2 : $()                                 // id: %3

} // end sil function 'NSObjectBase.NSObjectBase.Msg_ObjcX() -> ()'

// @objc NSObjectBase.Msg_ObjcX()

sil hidden [thunk] @@objc NSObjectBase.NSObjectBase.Msg_ObjcX() -> () : $@convention(objc_method) (NSObjectBase) -> () {

// %0                                             // users: %4, %3, %1

bb0(%0 : $NSObjectBase):

strong_retain %0 : $NSObjectBase                // id: %1

// function_ref NSObjectBase.Msg_ObjcX()

%2 = function_ref @NSObjectBase.NSObjectBase.Msg_ObjcX() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () // user: %3

%3 = apply %2(%0) : $@convention(method) (@guaranteed NSObjectBase) -> () // user: %5

strong_release %0 : $NSObjectBase               // id: %4

return %3 : $()                                 // id: %5

} // end sil function '@objc NSObjectBase.NSObjectBase.Msg_ObjcX() -> ()'

sil hidden @NSObjectBase.NSObjectBase.callTest() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () {

// %0                                             // users: %3, %2, %1

bb0(%0 : $NSObjectBase):

debug_value %0 : $NSObjectBase, let, name "self", argno 1 // id: %1

%2 = class_method %0 : $NSObjectBase, #NSObjectBase.Msg_Normal!1 : (NSObjectBase) -> () -> (), $@convention(method) (@guaranteed NSObjectBase) -> () // user: %3

%3 = apply %2(%0) : $@convention(method) (@guaranteed NSObjectBase) -> ()

%4 = tuple ()                                   // user: %5

return %4 : $()                                 // id: %5

} // end sil function 'NSObjectBase.NSObjectBase.callTest() -> ()'

// NSObjectBase.callAgain()

sil hidden @NSObjectBase.NSObjectBase.callAgain() -> () : $@convention(method) (@guaranteed NSObjectBase) -> () {

// %0                                             // users: %3, %2, %1

bb0(%0 : $NSObjectBase):

debug_value %0 : $NSObjectBase, let, name "self", argno 1 // id: %1

%2 = class_method %0 : $NSObjectBase, #NSObjectBase.Msg_Third!1 : (NSObjectBase) -> () -> (), $@convention(method) (@guaranteed NSObjectBase) -> () // user: %3

%3 = apply %2(%0) : $@convention(method) (@guaranteed NSObjectBase) -> ()

%4 = tuple ()                                   // user: %5

return %4 : $()                                 // id: %5

} // end sil function 'NSObjectBase.NSObjectBase.callAgain() -> ()'

sil_vtable NSObjectBase {

#NSObjectBase.Msg_Normal!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Normal() -> () // NSObjectBase.Msg_Normal()

#NSObjectBase.Msg_Second!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Second() -> () // NSObjectBase.Msg_Second()

#NSObjectBase.Msg_Third!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Third() -> ()// NSObjectBase.Msg_Third()

#NSObjectBase.Msg_Objc!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Objc() -> () // NSObjectBase.Msg_Objc()

#NSObjectBase.callTest!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.callTest() -> () // NSObjectBase.callTest()

#NSObjectBase.callAgain!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.callAgain() -> ()// NSObjectBase.callAgain()

}

sil_vtable DerivedOcClass {

#NSObjectBase.Msg_Normal!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Normal() -> () [inherited] // NSObjectBase.Msg_Normal()

#NSObjectBase.Msg_Second!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Second() -> () [inherited] // NSObjectBase.Msg_Second()

#NSObjectBase.Msg_Third!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Third() -> () [inherited] // NSObjectBase.Msg_Third()

#NSObjectBase.Msg_Objc!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.Msg_Objc() -> () [inherited] // NSObjectBase.Msg_Objc()

#NSObjectBase.callTest!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.callTest() -> () [inherited] // NSObjectBase.callTest()

#NSObjectBase.callAgain!1: (NSObjectBase) -> () -> () : @NSObjectBase.NSObjectBase.callAgain() -> () [inherited] // NSObjectBase.callAgain()

}

apply担任函数绑定和派发的职责

那么阅读就显得简单多了, 可以看到最终对应到 testFunc函数调用的指令有两条.

%4 = class_method %2 : $MyClass, #MyClass.testFunc!1 : (MyClass) -> () -> (), $@convention(method) (@guaranteed MyClass) -> () // user: %5
%5 = apply %4(%2) : $@convention(method) (@guaranteed MyClass) -> ()

1. class_method: 该指令通过类的函数表来查找函数, 基于类的实际类型.
2. apply: 传递参数并执行函数.

作者：MaizeJS
链接：https://www.jianshu.com/p/cfe7da01880d
来源：简书
简书著作权归作者所有，任何形式的转载都请联系作者获得授权并注明出处。