如下定義Student，在構(gòu)造函數(shù)傳入閉包。假設(shè)這個(gè)類(lèi)是已經(jīng)存在的，調(diào)用方無(wú)法修改；那調(diào)用時(shí)應(yīng)該注意避免循環(huán)引用

class Student{
        private var doWork:(()->())
        
        init(delegate:  @escaping (()->())){
            self.doWork = delegate
        }
        
        deinit {
            print("deinit student")
        }
    }

Teacher內(nèi)部持有Student，如果Student的構(gòu)造函數(shù)需要的閉包直接指向Teacher的成員方法，會(huì)發(fā)生循環(huán)引用

不應(yīng)該寫(xiě)為

myStudent = Student(delegate:classBegin)

需要把classBegin放到一個(gè)weak self的閉包中被呼叫才能避免循環(huán)引用

class Teacher{
        private func classBegin() {
            print("hi, classmates!")
        }
        
        private var myStudent : Student?
        
        func addStudent() {
            
            //這樣寫(xiě)無(wú)法釋放，會(huì)內(nèi)存泄露
            //myStudent = Student(delegate:classBegin)
            
             myStudent = Student(delegate: {
                [weak self] in
                self?.classBegin()
             })
        }
        
        deinit {
            print("deinit teacher")
        }
    }