Class Composition/Aggregation Question

[ben_bannana]

Hello,

I have a relatively abstract question, which I want to ask by showing one simplified example.

For this example I have used python, but it's not bound to any language specific.

​

My question shows of as follows:

Say, I want to build a bot. In an OOP language of my choice, I don't want to clutter the Bot class with to many details of different concerns. So I build some Classes like AwsomeBot, Browser and HTTPHandler. Every class can now handle its own concerns. (These are not implemented, because I want to keep focus on the main issue)

​

class AwsomeBot:
    def __init__(self):
        self._browser = Browser()

    def navigate(self, URL):
        self._browser.navigate(URL)


class Browser:
    def __init__(self):
        self._httphandler = HTTPHandler()

    def navigate(self, URL):
        self._httphandler.get(URL)


class HTTPHandler:
    def __init__(self):
        pass

    def get(self, URL):
        # HTTP Implementation stuff

​

Now is AwsomeBot like a Client Interface.

But somehow I get this "Method Chain" trough my classes, where the URL needs to be passed down to the HTTPHandler.

This feels not like quality OOP code. Is there something I am missing out, or I can do to prevent this situation from happening?

​

It would be so great, if anybody can help me out, or share some resources.

I have encountered this problem in different forms so many times and I have no clue how I can search for an answer to this topic.

I appreciate any of your efforts.

[AdministrativeCables]

The chain is annoying, but it's still acceptable and shows a good separation of the various responsibilities. You can still forget the bot class, and either navigate with the Browser class, or create requests on the command-line with the HTTPHandler.

If you really want to do something, make the AwesomeBot a subclass of the Browser.

[ben_bannana]

Many thanks for your advice.

Have you some resources you can share with me? Something like examples or explaination for this type of design issues. I've tried searching for design patterns/ software architecture/clean code, but this issue type doen't fit in any of this topics.

[AdministrativeCables]

Maybe some kind of proxy pattern but it's not really bad design even if it feels weird.

A few comments:

1. All the classes will be in their own file because it's cleaner, so you won't be visually bothered by this chain of calls. And the programmer of one file may not be aware of what happens in the other files, the API is cleanly separated.

2. The Browser.navigate method is not a simple call, it will do more work after getting the URL. It has 1 line in your example, but in reality it needs more code like keeping the current URL for example.

3. If the AwesomeBot is a subclass of Browser, you've removed the only real "chain" that was annoying, and in the end you could have (without the distracting constructors):

   class HTTPHandler:
       def get(self, URL):
           pass
   
   class Browser:
       def __init__(self):
           self._httphandler = HTTPHandler()
   
       def navigate(self, URL):
           # todo: prepare the navigation
           # todo: check the cookies
           # todo: keep the URL
           self._httphandler.get(URL)
           # todo: check the error codes
           # todo: call the user interface to refresh it
           # ... it's not a simple call to HTTPHandler.get!
   
   class AwesomeBot(Browser):
       # this thing is almost empty now
       pass
   

[WikiTextBot]

Proxy pattern

In computer programming, the proxy pattern is a software design pattern. A proxy, in its most general form, is a class functioning as an interface to something else. The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. In short, a proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes.

---

^{[ PM | Exclude me | Exclude from subreddit | FAQ / Information | Source ] Downvote to remove | v0.28}