Using 'private facades' to accessing protected members

[nerobotParticipant]

Working on component-based system I found a nice solution to access to protected code. So I can leave it protected not public for end user. So…

Explain by example.

Let’s we have a class named Component.

Monkey

Class Component Property gameObject:GameObject() Return _gameObject End Protected Field _gameObject:GameObject Nethod New() ' constructor is protected too End End

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Class Component   Property gameObject:GameObject() Return _gameObject End Protected Field _gameObject:GameObject Nethod New() ' constructor is protected too End End

• Each component must be associated with game object.
• We have to get access to game object but not change it directly
• So public field or property isn’t good here

Solution is using ‘private facade’ / bridge class to get acces to protected members.

• Private – means private section of a file, not a class
• Bridge should extends our needed class, so worked for non-final classes only

Let’s write such bridge

Monkey

' file&nbsp;GameObject.monkey2 Class GameObject Method AddComponent<T>:T() Where T Extends Component Local comp:=ComponentBridge_Go.NewComponent<T>() Local name:=Typeof( comp ).Name _components[name]=comp ComponentBridge_Go.SetGameObject( comp,Self ) Return comp End End Private ' make it abstact to deny instantiation Class ComponentBridge_Go Extends Component Abstract Function NewComponent<T>:T() Where T Extends Component Return New T ' protected constructor End Function SetGameObject( comp:Component,go:GameObject ) comp._gameObject=go ' protected field 'comp.OnAttached() End End

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' file&nbsp;GameObject.monkey2   Class GameObject   Method AddComponent<T>:T() Where T Extends Component Local comp:=ComponentBridge_Go.NewComponent<T>() Local name:=Typeof( comp ).Name _components[name]=comp ComponentBridge_Go.SetGameObject( comp,Self ) Return comp End   End   Private   ' make it abstact to deny instantiation   Class ComponentBridge_Go Extends Component Abstract Function NewComponent<T>:T() Where T Extends Component Return New T ' protected constructor End Function SetGameObject( comp:Component,go:GameObject ) comp._gameObject=go ' protected field 'comp.OnAttached() End End

We can’t get access to our Bridge‘s classes outside framework – them are private in files.

And we able to provide clean api for end users.

[coconParticipant]

Is this an actual design pattern?

I tried to make a simple example to understand it better.

Monkey

#Import "<std>" Using std.. Class Message Property Content:String() Return _content End Protected Field _content:String End Class MessageChanger Extends Message Abstract Function Set(message:Message, content:String) message._content = content End End Function Main() Local m := New Message MessageChanger.Set(m, "Hello World") Print(m.Content) End

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#Import  "<std>" Using std..   Class Message Property Content:String() Return _content End Protected Field _content:String End   Class MessageChanger Extends Message Abstract Function Set(message:Message, content:String) message._content = content End End   Function Main() Local m := New Message MessageChanger.Set(m, "Hello World") Print(m.Content) End

I had this question for quite some time, how to control the access of class contents by certain restrictions, this seems to do the trick nicely. However the only bummer -as I think of it- is that the Changer class needs to inherit from the actual object, I hope that there won’t be any problem with creating such inheritance.

[nerobotParticipant]

Limitation is – you can’t inherit if class is final.

In my case I want to access to protected but somewhere in inner scope. So I put such bridges to private section.

Also there is an Internal keyword that we can use inside of our modules to access private sections. Like friend keyword in c++.

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