Always return nil when swizzling

[TLHorse]

I wrote the code:

class MyClass {
    @objc func origA() {
        print(#function)
    }
    @objc func origB(_ arg1: Bool) {
        print(#function)
    }
}
class MyClassHook {
    @objc func myA() {
        print(#function)
    }
    @objc func myB(_ arg1: Bool) {
        print(#function)
    }
}
MyClass().origA() // prints: origA()
MyClass().origB() // prints: origB()

Swizzle(MyClass.self) {
    #selector(MyClass.origA) <-> #selector(MyClassHook.myA)
    #selector(MyClass.origB(_:)) <-> #selector(MyClassHook.myB(_:))
}

MyClass().origA() // prints: origA(), expected: myA()

MyClass().origB() // prints: origB(), expected: myB()

I swizzle the method in right way. After swizzle, I print origA() and origB(), I expected them to be myA() and myB(), but the console still print origA() and origB().

I run in debug mode and found that, in SwizzleSwift.swift, public struct Swizzle, there’ s a code;

guard
                let original = class_getInstanceMethod(type, SwizzlePair.original),
                let swizzled = class_getInstanceMethod(type, SwizzlePair.swizzled)
            else { return }

And this code always execute the else block, which means that original or swizzled is returning nil.

Why? Is there a problem in my code?