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Re: Singletons?


Well, my goal isn't to prevent you from using singletons or anything,
I was just sharing my point of view. 

(About your Localization
singleton - I'd expect a language change to be something done *to* the
localization object (e.g. method call on it that changes some of its
data), not it to be a completely different instance) 

As you have
probably seen already, in ooc we prefer to implement patterns from
existing syntax - it is imho the sign of a powerful and expressive
language that we can then keep small. Scala has a *lot* of syntax (very
much like C++0x), not all of which is necessary imho. Lisp is quite
extreme in its minimalist, but I like to think that ooc is somehow a
middle ground. 

That said - doesn't the last way I suggested to do
singletons satisfy you? It basically takes an underscore and one line to
turn a class into a kinda-singleton, usable a-la scala (ie. without
get()), e.g. MySingleton doStuff(). (And yes I forgot to tell - you can
do stuff like MySingleton := _MySingleton new() at the module level,
it'll just be a global) 


P.S: Don't forget to hit "Reply all". No
reason to keep this discussion personal :) 

On Wed, 29 Sep 2010
18:49:25 -0300, Damian  wrote:  

Yes I know about the "singleton is
evil" thing. I disagree. 
I would never pass around an instance
everywhere. Imagine a Localization singleton that it's main function is
to take a key and return the respective string in the correct language.
In certain applications that singleton will be used *everywhere* in the
code. How can you replace a singleton by passing around an instance?

At the first link you provide, there's a list of the problems a
singleton causes: 

a) Says nothing  
b and c) memory leak // not with
d) syntactic noise because most languages don't support it // I
think this is the only problem 
c) problems when subclassing // If the
language supports singletons, it should not allow subclassing. Why would
you do it?! 
f) says someting about static methods that makes no sense
to me. 

It also says that the main problem using singletons is that
it's against OO design. But I don't see how. 

I agree with your point
about wanting several resource managers, and maybe in that case the best
option is storing an instance in an instance variable, or a static
instance on a class. But why are you going to mess your code like that
when you know there can/will be just one instance of a resourceManager /
userManager / Localizator / etc. 

Anyway, I'm just writing my thought
about the topic, I'm not requesting a feature. 
With the time I will get
more used to code in ooc and maybe that's the whole thing. 


Wed, Sep 29, 2010 at 5:43 PM,  wrote:

Ahah, but that's where we
disagree. Believe me, I fully grasp the seduction potential of
singletons, and I'm guilty of having used them much in the past..

Others have said it before, and much better than me: 


Concerning your example, what if you want several resource managers
that have different options? (ie. memory quotas/timeout before freeing
old unreferenced stuff, different loading paths, maybe disable the cache
completely one of the managers for debugging? different levels of
logging and destination of logging message, etc.) 

When your brain
thinks of singletons, it automatically becomes stupid - and misses
opportunities to make your code more flexible, easier to maintain and
debug, and more natural. 

Passing around an instance isn't *that* bad
of an idea, and storing an instance in an instance variable isn't too
bad either. 

If you really really want to emulate the Scala way I guess
this would work marvelously: 

// -- cut

_MySingle: class {
instance vars
 init: func {
 // initialize

MySingle := _MySingle

// -- cut 

Then, MySingle would be the instance, as in Scala,
and nobody in his right mine will go instanciate _MySingle directly (the
underscore is usually a convention of "don't touch or I'll bite your
balls off" in ooc land - aka "pseudo-protected". It's not impossible
that at some point in the future, a compiler switch is implemented to
enforce the encapsulation of such attributes.) 


On Wed, 29 Sep
2010 17:13:08 -0300, Damian  wrote:  

Well, I don't know; it's one of
the features I love from scala. 
I find singletons useful *a lot* of
times. It's just an object that there will be only one instance in the
app and that can be accessed from anywhere in the code.  
To me it's
useful for example to create a manager of resources, that has internal
cache, and where I can ask for a resource and the manager will look for
it in the cache or load it, process it, and chache it, and that kind of
I hate the pattern as you describe it too, because MySingle
should be the instance, not a class, and I should be abble to do
something like: 
Resources getResource("nana") 
instead of 
getInstance() getResource("nana") 
I think that the namespaced imports
are more suitable... Though I don't like it too much to be honest. But
well, ooc is not 100% object oriented and maybe it's just that I'm not
used to that.  

By the way, is there any documentation about namespaced

On Wed, Sep 29, 2010 at 3:58 PM,  wrote:

 Well singletons are
more than namespaces, although I kinda hate this
 pattern, here it

 you can choose to implement 'new' as your get method:

MySingle: class {

 _instance := static alloc() as This
 new: static
func -> This { _instance }


 if you dislike this (because 'new'
sortof implies that it's a new
 instance..) just use 'get' instead of
'new', there's not really a
 convention here yet

 also, there's no
special syntax like Scala's object: I actually dislike
 this bit of
Scala's syntax, it's mostly useful for the main class in
 Scala anyway..
(correct me if I'm wrong).


 On Wed, 29 Sep 2010 14:33:01 -0400,

> Easy: Don't.
 > ooc != Java
 > If you want a
namespace sort of effect, just use namespaced imports:
 > import
Source/Path/Foo into Foo
 > Foo doSomeStuff(10)
 > If you can't
use namespaced imports (for one-file-monsters), use a
 > cover's static
 > Foo: cover{
 > doSomeStuff: static func(argument: Int)
 > Foo doSomeStuff(10)
 > On Sep 28, 2010, at 1:16 PM, Damian 
 >> What's the proper or preferred way to create a singleton
in ooc? Is > there something specific to do so? (like 'object' in scala,
for > example)
 >> Thanks!
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 > Mailing list:
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