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) -> ()
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.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
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