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Traits for class methods?

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khinsen

Traits for class methods?

Hi everyone,

A quick question: is it possible to use traits to define class methods?

For example, could the popular singleton pattern consisting of the
three class methods #uniqueInstance, #new, and #reset plus the instance
variable uniqueInstance be packaged as a trait?

Konrad.

CyrilFerlicot

Re: Traits for class methods?

On Mon, Feb 11, 2019 at 4:50 PM Konrad Hinsen
<[hidden email]> wrote:
>
> Hi everyone,
>
> A quick question: is it possible to use traits to define class methods?
>
> For example, could the popular singleton pattern consisting of the
> three class methods #uniqueInstance, #new, and #reset plus the instance
> variable uniqueInstance be packaged as a trait?

Hi,

Yes it is possible.

>
> Konrad.
>

--
Cyril Ferlicot
https://ferlicot.fr

Vitor Medina Cruz

Re: Traits for class methods?

It seems, however, that self points to the trait class, instead of the target object class. Is that correct? Instance side methods behave as expected and self points to the target object.

On Mon, Feb 11, 2019 at 2:19 PM Cyril Ferlicot <[hidden email]> wrote:

On Mon, Feb 11, 2019 at 4:50 PM Konrad Hinsen
<[hidden email]> wrote:
>
> Hi everyone,
>
> A quick question: is it possible to use traits to define class methods?
>
> For example, could the popular singleton pattern consisting of the
> three class methods #uniqueInstance, #new, and #reset plus the instance
> variable uniqueInstance be packaged as a trait?

Hi,

Yes it is possible.

>
> Konrad.
>

--
Cyril Ferlicot
https://ferlicot.fr

Vitor Medina Cruz

Re: Traits for class methods?

Rectifying, It does as expected and self points to the target class. This odd behavior happened to me when I implemented the initialize method on the class side of a Trait and then clicked the 'Run Script' Button on the target class.

On Mon, Feb 11, 2019 at 4:52 PM Vitor Medina Cruz <[hidden email]> wrote:

It seems, however, that self points to the trait class, instead of the target object class. Is that correct? Instance side methods behave as expected and self points to the target object.

On Mon, Feb 11, 2019 at 2:19 PM Cyril Ferlicot <[hidden email]> wrote:
On Mon, Feb 11, 2019 at 4:50 PM Konrad Hinsen
<[hidden email]> wrote:
>
> Hi everyone,
>
> A quick question: is it possible to use traits to define class methods?
>
> For example, could the popular singleton pattern consisting of the
> three class methods #uniqueInstance, #new, and #reset plus the instance
> variable uniqueInstance be packaged as a trait?

Hi,

Yes it is possible.

>
> Konrad.
>

--
Cyril Ferlicot
https://ferlicot.fr

HilaireFernandes

Re: Traits for class methods?

In reply to this post by khinsen

With singleton you will access class variable, which you can't with a
trait, so you will need a setter, but should work I guess

Hilaire

--
Dr. Geo
http://drgeo.eu

http://drgeo.eu

CyrilFerlicot

Re: Traits for class methods?

On Mon 11 Feb 2019 at 20:36, Hilaire <[hidden email]> wrote:

With singleton you will access class variable, which you can't with a
trait, so you will need a setter, but should work I guess

Hi,

Since Pharo 7, Traits are statefuls.

See documentation at:

https://github.com/pharo-open-documentation/pharo-wiki/blob/master/General/Traits.md

Hilaire

--
Dr. Geo
http://drgeo.eu

Cyril Ferlicot
https://ferlicot.fr

HilaireFernandes

Re: Traits for class methods?

Thanks for the update. Took a look at the doc bellow. To my taste, this
traits design really add complexity in the code, particularly in
responsibility and now the state. While it could be useful in some
situation.

Le 11/02/2019 à 20:37, Cyril Ferlicot a écrit :
> Hi,
>
> Since Pharo 7, Traits are statefuls.
>
> See documentation at:
> https://github.com/pharo-open-documentation/pharo-wiki/blob/master/General/Traits.md
>
--
Dr. Geo
http://drgeo.eu

http://drgeo.eu

khinsen

Re: Traits for class methods?

In reply to this post by CyrilFerlicot

On 11/02/2019 17:18, Cyril Ferlicot wrote:

> A quick question: is it possible to use traits to define class methods?
>> For example, could the popular singleton pattern consisting of the
>> three class methods #uniqueInstance, #new, and #reset plus the instance
>> variable uniqueInstance be packaged as a trait?
> Hi,
>
> Yes it is possible.

Thanks for your encouragement!

I ended up trying exactly that example, and it works just fine:

https://github.com/khinsen/SingletonTrait

Konrad.

Marcus Denker-4

Re: Traits for class methods?

> On 13 Feb 2019, at 12:22, Konrad Hinsen <[hidden email]> wrote:
>
> On 11/02/2019 17:18, Cyril Ferlicot wrote:
>
>> A quick question: is it possible to use traits to define class methods?
>>> For example, could the popular singleton pattern consisting of the
>>> three class methods #uniqueInstance, #new, and #reset plus the instance
>>> variable uniqueInstance be packaged as a trait?
>> Hi,
>>
>> Yes it is possible.
>
> Thanks for your encouragement!
>
> I ended up trying exactly that example, and it works just fine:
>
> https://github.com/khinsen/SingletonTrait
>

It is amazing how much better this feels now that Traits can define state, too… (compared to before where it was just methods).

https://github.com/khinsen/SingletonTrait/blob/master/SingletonTrait/SingletonTrait.trait.st

I would even want to have (and use) a Trait like that in the system by default.

Marcus

HilaireFernandes

Re: Traits for class methods?

I am wondering. Does it not make responsabilities less clear, shareed in
class hierarchy and traits hierarchy, now both in term of behavior but
also state?

Hilaire

Le 13/02/2019 à 13:02, Marcus Denker a écrit :
> It is amazing how much better this feels now that Traits can define state, too… (compared to before where it was just methods).
>
> https://github.com/khinsen/SingletonTrait/blob/master/SingletonTrait/SingletonTrait.trait.st
>
> I would even want to have (and use) a Trait like that in the system by default.
>
> Marcus

--
Dr. Geo
http://drgeo.eu

http://drgeo.eu

CyrilFerlicot

Re: Traits for class methods?

On Wed, Feb 13, 2019 at 2:40 PM Hilaire <[hidden email]> wrote:
>
> I am wondering. Does it not make responsabilities less clear, shareed in
> class hierarchy and traits hierarchy, now both in term of behavior but
> also state?
>

Hi,

In general I do not choose between inheritance and composition based
on what the language allows. When we had stateless traits, I created
subclasses even if I was not using any state, because it made sense.

I'm not a big fan of limiting the language on composition because the
choice between composition and inheritance should be conceptual and
not technical.

I read in an article this way to choose between inheritance and composition:

«Inheritance should only be used when:
- Both classes are in the same logical domain
- The subclass is a proper subtype of the superclass
- The superclass’s implementation is necessary or appropriate for the subclass
- The enhancements made by the subclass are primarily additive.»

> Hilaire
>
> --
> Dr. Geo
> http://drgeo.eu
>
>
>

--
Cyril Ferlicot
https://ferlicot.fr

Herby Vojčík

Re: Traits for class methods?

On 13. 2. 2019 14:54, Cyril Ferlicot wrote:

> On Wed, Feb 13, 2019 at 2:40 PM Hilaire <[hidden email]> wrote:
>>
>> I am wondering. Does it not make responsabilities less clear, shareed in
>> class hierarchy and traits hierarchy, now both in term of behavior but
>> also state?
>>
>
> Hi,
>
> In general I do not choose between inheritance and composition based
> on what the language allows. When we had stateless traits, I created
> subclasses even if I was not using any state, because it made sense.
>
> I'm not a big fan of limiting the language on composition because the
> choice between composition and inheritance should be conceptual and
> not technical.

Sorry for the unconstructive and spammy "I like it" post, but:

+1!

> I read in an article this way to choose between inheritance and composition:
>
> «Inheritance should only be used when:
> - Both classes are in the same logical domain
> - The subclass is a proper subtype of the superclass
> - The superclass’s implementation is necessary or appropriate for the subclass
> - The enhancements made by the subclass are primarily additive.»
>
>> Hilaire
>>
>> --
>> Dr. Geo
>> http://drgeo.eu

khinsen

Re: Traits for class methods?

In reply to this post by Marcus Denker-4

Marcus Denker <[hidden email]> writes:

> It is amazing how much better this feels now that Traits can define state, too… (compared to before where it was just methods).
>
> https://github.com/khinsen/SingletonTrait/blob/master/SingletonTrait/SingletonTrait.trait.st
>
> I would even want to have (and use) a Trait like that in the system by default.

That's what I thought as well when I saw the 43 implementors of
uniqueInstance in Pharo.

I'll package this as a pull request for Pharo!

Konrad.

Stephan Eggermont-3

Re: Traits for class methods?

In reply to this post by CyrilFerlicot

Cyril Ferlicot <[hidden email]>
wrote:
>
> I'm not a big fan of limiting the language on composition because the
> choice between composition and inheritance should be conceptual and
> not technical.
>
> I read in an article this way to choose between inheritance and composition:

An alternative (Smalltalk) view is that inheritance is primarily a code
reuse instrument. Use it when it allows you to do so. Java and c++ deformed
a lot of OO thinking

Stephan