Comments on: The Issues With Singletons and How to Fix Them

By: Jonathan Boccara

Jonathan Boccara — Sun, 18 Mar 2018 19:50:00 +0000

In reply to shaik shami. Shaik, just in case you weren't notified, note that Mihai answered your comment here. Thanks!

By: Mihai Sebea

Mihai Sebea — Sat, 17 Mar 2018 17:56:00 +0000

In reply to f_zweig. Well the game class here is just an example of the point that I was trying to make: that some classes should not know about each other and some other class ie the game can connect them ... It s not meant as a production ready class. I suppose if you would want to test the game class you would have a factory method that would create what ever classes are needed to be mocked

By: f_zweig

f_zweig — Fri, 16 Mar 2018 20:37:00 +0000

In reply to Mihai Sebea. How would you create an instance of the Game class with mock logger, mock debugger and/or mock profiler? You can't, because they are part of the class and cannot be set/replaced from outside. Or am I missing something fundamental here?

By: Mihai Sebea

Mihai Sebea — Fri, 16 Mar 2018 19:58:00 +0000

In reply to f_zweig. What can of problem would you have with mock objects ? The problem that i see in passing objects in the constructor is that in introduces too much coupling !

By: f_zweig

f_zweig — Fri, 16 Mar 2018 10:14:00 +0000

Speaking of testing, I feel like the third solution will have issues when trying to replace the logger, debugger, or profiler with mock objects. In the second approach, I can just pass mock instances through the constructor. There’s no way to do that in the third approach.

So I think the best would be to combine those two, and have the objects to which you want to connect passed via constructor (c.f. dependency injection).

By: Антон

Антон — Thu, 15 Mar 2018 13:38:00 +0000

In reply to Mihai Sebea. In such a 'cross-dependency' case it doesn't matter whether logger and filesystem are singletons or not. You have to solve the dependency first and then you'll find singletons are still fine!

By: Gil

Gil — Fri, 09 Mar 2018 11:16:00 +0000

Here is a great talk about global state and singletons from google:
https://www.youtube.com/watch?v=-FRm3VPhseI
Basically, you very rarely need a true Singleton, more often you just need a *single instance* of some class (which you can pass around without actually restricting instantiation).

By: Mihai Sebea

Mihai Sebea — Thu, 08 Mar 2018 20:54:00 +0000

Hi
what I was trying to say is that it might be ok if you had ONLY one system as a singleton … like the logger ..or the filesystem. What happens in practice is that you have multiple systems as singletons . You will have the logger , the filesystem, the keyboard the display and probably many others. And by they will depend on each other I mean that the logger class might need access to the filesystem in order to log to a file but the filesystem might need the logger to log when a file is opened.
I hope this explains this a bit better !

By: shaik shami

shaik shami — Thu, 08 Mar 2018 18:08:00 +0000

Hello,

I didn’t get the context
“But in my experience you never have just one system as a singleton. You have multiple occurrences of them and at some point they will depend on each other.”
Could you please explain in-detail ?