Comments on: To “new” or not to “new”…

By: misko

misko — Mon, 08 Feb 2010 02:56:29 +0000

@ Juraj,

I would solve this in this way

interface Output;
class Speaker implements Output;
class Headset implements Output;
class OutputSelector(Speaker, Headset) implements Output;
class MusicPlayer(Output);

s = new Speaker()
h = new Headset()
os = new OutputSerector(s, h);
mp = new MusicPlayer(os);

os.seletOutput(…);
wp.play();

By: Juraj Blahunka

Juraj Blahunka — Sun, 07 Feb 2010 00:15:55 +0000

@Misko What about injectables, that are required for object instantiation but can be changed with another values? (like your MusicPlayer, which needs AudioDevice)… Sure AudioDevice is needed in MusicPlayer’s constructor, but AudioDevice can change (from Speakers to Headset).. Should a SETTER be introduced? Doesn’t this bring ambiguity to the MusicPlayer class?

By: Koen

Koen — Thu, 17 Dec 2009 17:24:12 +0000

A database connection is an injectable. Yet the user credentials are newables. Unless you call db->connect(credentials). But that’s not really the job of the dependency injection container. So it seems like there are case in which the theory doesn’t hold.

By: miw

miw — Fri, 04 Dec 2009 22:29:21 +0000

Hi,

@Sam

Good point Sam, I also came to this conclusion and would like to hear about it.

By: Sam

Sam — Mon, 30 Nov 2009 21:49:51 +0000

Hi Misko,
I have a simple question. Because an injectable can never have a newable as a constructor parameter, at some point there must be an injectable implementation which has a parameterless constructor, right?

By: Making Zend_Auth more “Object Oriented” | Aviblock.com

Making Zend_Auth more “Object Oriented” | Aviblock.com — Fri, 30 Oct 2009 01:13:09 +0000

[...] the Zend_Auth_Adapter_Interface. It seems to me that it violates one of Misko’s rules that injectables can depend on injectables, and newables can depend on newables, but the twain shall not …. So if my understanding of that rule is correct, $adapter->setIdentity($thisvarisanewable), would [...]

By: All About Google » How to think about OO

All About Google » How to think about OO — Tue, 06 Oct 2009 06:42:34 +0000

[...] Should User have a field reference to Ldap? The answer is no, because you may want to serialize the user to database but you don’t want to serialize the Ldap. See here. [...]

By: Marty

Marty — Thu, 10 Sep 2009 07:04:09 +0000

I’m still not really can follow this

If your requirements now say that MusicPlayer has to have a name (String field) – it becomes a Newable and its not injectable anymore ?
So what to do with the current MusicPlayer, because it also has the AudioAdvice field – and the injection fails…

what is the solution for that ?

By: Design for Testability and “Domain-Driven Design”

Design for Testability and “Domain-Driven Design” — Tue, 17 Mar 2009 05:35:10 +0000

[...] I have a question about your distinction between “newable”, value classes and “injectable” or “service” classes. [...]

By: Don Vince

Don Vince — Tue, 30 Dec 2008 14:00:20 +0000

Great article, I’ve been trying to wrap my head around the subtleties.For a Logger class, an Injectable (a good sell on that can be found here: http://misko.hevery.com/code-reviewers-guide/flaw-brittle-global-state-singletons/ ) I can see that all/most the Injectable’s will have the Logger as a constructor parameter and will be merrily logging away to the object.What I’m not sure about is when a newable wants to do it’s logging.I think I could:Put the logger on the signature every method that does some logging (feels ugly)Ensure the newable’s have a fantastic ToString() method and let the Injectable’s do all the logging (feels nicer)Any further suggestions out there?