问题实现观察者模式：“成员引用基类型________不是结构或联合体” [英] Problem Implementing Observer Pattern : "Member reference base type ________ is not a structure or union"

问题描述

我一直在实现一个准系统观察者模式，并且停留在一个有点神秘的错误：
成员引用基类型Observer *'不是一个结构或联合。我假设这与我使用的模板有关，我仍然相当不舒服。这里是冒犯的代码（最简单的消除了大部分cons / destructors简化的东西）：

I've been implementing a barebones observer pattern and am stuck on a somewhat cryptic error: "Member reference base type 'Observer *' is not a structure or union". I assume this has something to do with my use of templates, with which I'm still fairly uncomfortable. Here is the offending code (most cons/destructors removed to simplify things):

主题界面：

class Subject { 
public:
    virtual void notify();
private:
    list< Observer * > m_observers; 
};

主题实施：

void Subject::notify() {
    list< Observer * >::iterator i;

    for ( i = m_observers.begin(); i != m_observers.end(); i++ ) {
        *i->update( this );                        // ERROR !!! ERROR
}

Observer抽象接口：

Observer abstract interface:

class Observer {
public:
    virtual ~Observer();
    virtual void update( Subject * changedSubject ) = 0;

protected:
    Observer();
};

具体观察者界面：

class ConcreteObserver: public Observer {

public:
    ConcreteObserver( ConcreteSubject * );
    virtual ~ConcreteObserver();

    virtual void update( Subject * changedSubject );

private:
    ConcreteSubject * m_subject;
};

具体观察者实施：

void ConcreteObserver::update( Subject * changedSubject ) {
    if ( changedSubject == m_subject ) {
        report();
    }
}

如果任何人可以帮助识别这个问题，非常感谢。

If anyone could help identify this problem, I would greatly appreciate it.

干杯，
Nick

Cheers, Nick

推荐答案

问题是用操作符优先级。而不是：

The problem is with the operator precedence. Instead of:

*i->update( this );

使用：

(*i)->update( this );

否则，将被解释为 *（i-> update this）），试图调用指针上的方法，导致错误消息。

Otherwise, it will be interpreted as *(i->update( this )), which tries to call a method on a pointer, resulting in the error message.

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