# Overriding new?

**URL:** <https://rubytalk.org/t/overriding-new/57769>\
**Category:** ruby-talk\
**Created:** [15 March 2010 14:13 UTC](https://rubytalk.org/t/overriding-new/57769 "2010-03-15T14:13:16Z")\
**Posts on this page:** 19\
**Page:** 1

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 14:13 UTC](https://rubytalk.org/t/overriding-new/57769/1 "2010-03-15T14:13:16Z")

</div>

Hi everybody,

&nbsp;&nbsp;given the following situation:

class Parent

&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;print "magic\n"  
&nbsp;&nbsp;end

end

class Child \< Parent

&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;print "more magic\n"  
&nbsp;&nbsp;end

end

child = Child.new

is there a way in which i can get "magic" and "more magic" as the  
output, without having to add super to the child class's constructor? I  
was thinking about overriding the class method "new" but i really didn't  
get anything to work up to now.

Any suggestions? Thanks in advance!

> **···**
>
> --  
> Andrea Dallera
> 
> > **[bolthar/freightrain](https://github.com/bolthar/freightrain)**
> >
> > freightrain - Ruby desktop development made easy
> 
>   
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog

---

<div class="post-metadata">

**Author:** ![Chuck\_Remes](https://avatars.discourse-cdn.com/v4/letter/c/3be4f8/32.png) [@Chuck\_Remes](https://rubytalk.org/u/Chuck_Remes)\
**Post date:** [15 March 2010 14:32 UTC](https://rubytalk.org/t/overriding-new/57769/2 "2010-03-15T14:32:15Z")

</div>

Use the #super keyword to call the superclass.

class Parent  
&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;print "magic\n"  
&nbsp;&nbsp;end  
end

class Child \< Parent  
&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;super  
&nbsp;&nbsp;&nbsp;&nbsp;print "more magic\n"  
&nbsp;&nbsp;end  
end

child = Child.new

> **···**
>
> On Mar 15, 2010, at 9:13 AM, Andrea Dallera wrote:
> 
> > Hi everybody,
> > 
> > &nbsp;&nbsp;given the following situation:
> > 
> > class Parent
> > 
> > def initialize  
> > &nbsp;&nbsp;&nbsp;print "magic\n"  
> > end
> > 
> > end
> > 
> > class Child \< Parent
> > 
> > def initialize  
> > &nbsp;&nbsp;&nbsp;print "more magic\n"  
> > end
> > 
> > end
> > 
> > child = Child.new
> > 
> > is there a way in which i can get "magic" and "more magic" as the  
> > output, without having to add super to the child class's constructor? I  
> > was thinking about overriding the class method "new" but i really didn't  
> > get anything to work up to now.
> 
> ----------
> 
> cremes$ ruby a.rb  
> magic  
> more magic
> 
> cr

---

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 14:41 UTC](https://rubytalk.org/t/overriding-new/57769/3 "2010-03-15T14:41:57Z")

</div>

Hei Chuck,

&nbsp;&nbsp;that's exactly what i was trying to avoid. While I'm at it, let me be  
more specific about my problem, which is actually not just printing out  
text to the console but changing the state of the newly created  
instance:

class Parent

&nbsp;&nbsp;attr\_reader :test\_value  
&nbsp;&nbsp;  
&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;@test\_value = "from parent"  
&nbsp;&nbsp;end

end

class Child \< Parent

&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;p @test\_value  
&nbsp;&nbsp;end  
&nbsp;&nbsp;  
end

child = Child.new

this should print out "from parent"

> **···**
>
> --  
> Andrea Dallera
> 
> > **[GitHub - bolthar/freightrain: Ruby desktop development made easy](https://github.com/bolthar/freightrain)**
> >
> > Ruby desktop development made easy. Contribute to bolthar/freightrain development by creating an account on GitHub.
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog
> 
> On Mon, 2010-03-15 at 23:32 +0900, Chuck Remes wrote:
> 
> > On Mar 15, 2010, at 9:13 AM, Andrea Dallera wrote:
> 
> > \> Hi everybody,  
> > \>  
> > \> given the following situation:  
> > \>  
> > \> class Parent  
> > \>  
> > \> def initialize  
> > \> print "magic\n"  
> > \> end  
> > \>  
> > \> end  
> > \>  
> > \> class Child \< Parent  
> > \>  
> > \> def initialize  
> > \> print "more magic\n"  
> > \> end  
> > \>  
> > \> end  
> > \>  
> > \> child = Child.new  
> > \>  
> > \> is there a way in which i can get "magic" and "more magic" as the  
> > \> output, without having to add super to the child class's constructor? I  
> > \> was thinking about overriding the class method "new" but i really didn't  
> > \> get anything to work up to now.
> > 
> > Use the #super keyword to call the superclass.
> > 
> > class Parent  
> > &nbsp;&nbsp;def initialize  
> > &nbsp;&nbsp;&nbsp;&nbsp;print "magic\n"  
> > &nbsp;&nbsp;end  
> > end
> > 
> > class Child \< Parent  
> > &nbsp;&nbsp;def initialize  
> > &nbsp;&nbsp;&nbsp;&nbsp;super  
> > &nbsp;&nbsp;&nbsp;&nbsp;print "more magic\n"  
> > &nbsp;&nbsp;end  
> > end
> > 
> > child = Child.new
> > 
> > ----------
> > 
> > cremes$ ruby a.rb  
> > magic  
> > more magic
> > 
> > cr

---

<div class="post-metadata">

**Author:** ![Marvin\_GA\_lker](https://avatars.discourse-cdn.com/v4/letter/m/e95f7d/32.png) [@Marvin\_GA\_lker](https://rubytalk.org/u/Marvin_GA_lker)\
**Post date:** [15 March 2010 14:50 UTC](https://rubytalk.org/t/overriding-new/57769/4 "2010-03-15T14:50:04Z")

</div>

Andrea Dallera wrote:

> this should print out "from parent"

Maybe I can't follow you, but that's exactly what's super for:

> **···**
>
> -------------------------------------------  
> irb(main):001:0\> class Parent  
> irb(main):002:1\> attr\_reader :test\_value  
> irb(main):003:1\> def initialize  
> irb(main):004:2\> @test\_value = "from parent"  
> irb(main):005:2\> end  
> irb(main):006:1\> end  
> =\> nil  
> irb(main):007:0\> class Child \< Parent  
> irb(main):008:1\> def initialize  
> irb(main):009:2\> super  
> irb(main):010:2\> p @test\_value  
> irb(main):011:2\> end  
> irb(main):012:1\> end  
> =\> nil  
> irb(main):013:0\> child = Child.new  
> "from parent"  
> =\> #\<Child:0x0000000183c140 @test\_value="from parent"\>  
> irb(main):014:0\>  
> -------------------------------------------  
> Why don't you want it?
> 
> Marvin  
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![Jason\_W1](https://avatars.discourse-cdn.com/v4/letter/j/ed8c4c/32.png) [@Jason\_W1](https://rubytalk.org/u/Jason_W1)\
**Post date:** [15 March 2010 14:50 UTC](https://rubytalk.org/t/overriding-new/57769/5 "2010-03-15T14:50:15Z")

</div>

def initialize  
&nbsp;&nbsp;&nbsp;p @test\_value = super  
end

?

> **···**
>
> On Mon, Mar 15, 2010 at 2:41 PM, Andrea Dallera \<andrea@andreadallera.com\>wrote:
> 
> > Hei Chuck,
> > 
> > &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;that's exactly what i was trying to avoid. While I'm at it, let me  
> > be  
> > more specific about my problem, which is actually not just printing out  
> > text to the console but changing the state of the newly created  
> > instance:
> > 
> > class Parent
> > 
> > attr\_reader :test\_value
> > 
> > def initialize  
> > &nbsp;&nbsp;&nbsp;@test\_value = "from parent"  
> > &nbsp;&nbsp;end
> > 
> > end
> > 
> > class Child \< Parent
> > 
> > def initialize  
> > &nbsp;&nbsp;&nbsp;&nbsp;p @test\_value  
> > &nbsp;&nbsp;end
> > 
> > end
> > 
> > child = Child.new
> > 
> > this should print out "from parent"
> > 
> > --  
> > Andrea Dallera  
> > [GitHub - bolthar/freightrain: Ruby desktop development made easy](http://github.com/bolthar/freightrain)  
> > [http://usingimho.wordpress.com](http://usingimho.wordpress.com)
> > 
> > On Mon, 2010-03-15 at 23:32 +0900, Chuck Remes wrote:  
> > \> On Mar 15, 2010, at 9:13 AM, Andrea Dallera wrote:
> > 
> > \> \> Hi everybody,  
> > \> \>  
> > \> \> given the following situation:  
> > \> \>  
> > \> \> class Parent  
> > \> \>  
> > \> \> def initialize  
> > \> \> print "magic\n"  
> > \> \> end  
> > \> \>  
> > \> \> end  
> > \> \>  
> > \> \> class Child \< Parent  
> > \> \>  
> > \> \> def initialize  
> > \> \> print "more magic\n"  
> > \> \> end  
> > \> \>  
> > \> \> end  
> > \> \>  
> > \> \> child = Child.new  
> > \> \>  
> > \> \> is there a way in which i can get "magic" and "more magic" as the  
> > \> \> output, without having to add super to the child class's constructor? I  
> > \> \> was thinking about overriding the class method "new" but i really  
> > didn't  
> > \> \> get anything to work up to now.  
> > \>  
> > \> Use the #super keyword to call the superclass.  
> > \>  
> > \>  
> > \> class Parent  
> > \> def initialize  
> > \> print "magic\n"  
> > \> end  
> > \> end  
> > \>  
> > \> class Child \< Parent  
> > \> def initialize  
> > \> super  
> > \> print "more magic\n"  
> > \> end  
> > \> end  
> > \>  
> > \> child = Child.new  
> > \>  
> > \> ----------  
> > \>  
> > \> cremes$ ruby a.rb  
> > \> magic  
> > \> more magic  
> > \>  
> > \> cr  
> > \>  
> > \>
> 
> --  
> jbw

---

<div class="post-metadata">

**Author:** ![Chuck\_Remes](https://avatars.discourse-cdn.com/v4/letter/c/3be4f8/32.png) [@Chuck\_Remes](https://rubytalk.org/u/Chuck_Remes)\
**Post date:** [15 March 2010 14:59 UTC](https://rubytalk.org/t/overriding-new/57769/6 "2010-03-15T14:59:42Z")

</div>

Ah, I didn't read your original email very closely.

I don't know how to accomplish that without #super. There might be a way to modify the parent's meta class and then have the child pick up that value, but I'm not really sure how to do it.

cr

> **···**
>
> On Mar 15, 2010, at 9:41 AM, Andrea Dallera wrote:
> 
> > Hei Chuck,
> > 
> > &nbsp;&nbsp;that's exactly what i was trying to avoid. While I'm at it, let me be  
> > more specific about my problem, which is actually not just printing out  
> > text to the console but changing the state of the newly created  
> > instance:

---

<div class="post-metadata">

**Author:** ![Tony\_Arcieri6](https://avatars.discourse-cdn.com/v4/letter/t/ecccb3/32.png) [@Tony\_Arcieri6](https://rubytalk.org/u/Tony_Arcieri6)\
**Post date:** [15 March 2010 17:07 UTC](https://rubytalk.org/t/overriding-new/57769/7 "2010-03-15T17:07:14Z")

</div>

One way to avoid it is to override new. You can use the "allocate" method  
to create a new object instance without invoking its constructor. Name the  
superclass's "initialize" method something different, like preinitialize,  
and invoke that yourself. Be sure to invoke initialize too, if it's  
defined.

I've used this approach in frameworks where I intend for users to subclass,  
but my general impression nowadays is I should use a lot cleaner base class  
that doesn't need these sorts of hax, or not expect users to ever define  
their own constructor.

> **···**
>
> On Mon, Mar 15, 2010 at 7:41 AM, Andrea Dallera \<andrea@andreadallera.com\>wrote:
> 
> > Hei Chuck,
> > 
> > &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;that's exactly what i was trying to avoid.
> 
> --  
> Tony Arcieri  
> Medioh! A Kudelski Brand

---

<div class="post-metadata">

**Author:** ![Aldric\_Giacomoni2](https://avatars.discourse-cdn.com/v4/letter/a/91b2a8/32.png) [@Aldric\_Giacomoni2](https://rubytalk.org/u/Aldric_Giacomoni2)\
**Post date:** [15 March 2010 15:02 UTC](https://rubytalk.org/t/overriding-new/57769/8 "2010-03-15T15:02:13Z")

</div>

Chuck Remes wrote:

> **···**
>
> > On Mar 15, 2010, at 9:41 AM, Andrea Dallera wrote:
> > 
> > > Hei Chuck,
> > > 
> > > &nbsp;&nbsp;that's exactly what i was trying to avoid. While I'm at it, let me be  
> > > more specific about my problem, which is actually not just printing out  
> > > text to the console but changing the state of the newly created  
> > > instance:
> 
> Andrea:  
> I think something similar was brought up on this mailing  
> list/forum/newsgroup within the last two weeks or so. Take a look  
> through the older topics.  
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 15:04 UTC](https://rubytalk.org/t/overriding-new/57769/9 "2010-03-15T15:04:59Z")

</div>

Hi everybody,

&nbsp;&nbsp;the whole issues comes from here:  
[http://github.com/bolthar/freightrain/blob/master/lib/freightrain/freight\_view\_model.rb](http://github.com/bolthar/freightrain/blob/master/lib/freightrain/freight_view_model.rb)  
FreightViewModel is part of the framework, and if you're using it that's  
the way you should do it:

class MyViewModel \< FreightViewModel

...

end

what i don't like is that if you want to make \_your\_ viewmodel do stuff  
on initialize, which is usual, you have to write your initialize method  
as such:

def initialize  
&nbsp;&nbsp;super  
&nbsp;&nbsp;#your stuff here  
end

otherwise the automagical initialization (like building views, hooking  
to services, etc) doesn't work, because the constructor of  
FreightViewModel (that is the one taking care of all this) doesn't get  
called.  
I know this is not extremely important (you just have to remind to call  
super) but i'd prefer not to have that hassle : i forget it myself more  
than often.

> **···**
>
> --  
> Andrea Dallera
> 
> > **[GitHub - bolthar/freightrain: Ruby desktop development made easy](https://github.com/bolthar/freightrain)**
> >
> > Ruby desktop development made easy. Contribute to bolthar/freightrain development by creating an account on GitHub.
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog
> 
> On Mon, 2010-03-15 at 23:50 +0900, Marvin Gülker wrote:
> 
> > Andrea Dallera wrote:  
> > \> this should print out "from parent"
> > 
> > Maybe I can't follow you, but that's exactly what's super for:  
> > -------------------------------------------  
> > irb(main):001:0\> class Parent  
> > irb(main):002:1\> attr\_reader :test\_value  
> > irb(main):003:1\> def initialize  
> > irb(main):004:2\> @test\_value = "from parent"  
> > irb(main):005:2\> end  
> > irb(main):006:1\> end  
> > =\> nil  
> > irb(main):007:0\> class Child \< Parent  
> > irb(main):008:1\> def initialize  
> > irb(main):009:2\> super  
> > irb(main):010:2\> p @test\_value  
> > irb(main):011:2\> end  
> > irb(main):012:1\> end  
> > =\> nil  
> > irb(main):013:0\> child = Child.new  
> > "from parent"  
> > =\> #\<Child:0x0000000183c140 @test\_value="from parent"\>  
> > irb(main):014:0\>  
> > -------------------------------------------  
> > Why don't you want it?
> > 
> > Marvin

---

<div class="post-metadata">

**Author:** ![Chuck\_Remes](https://avatars.discourse-cdn.com/v4/letter/c/3be4f8/32.png) [@Chuck\_Remes](https://rubytalk.org/u/Chuck_Remes)\
**Post date:** [15 March 2010 17:24 UTC](https://rubytalk.org/t/overriding-new/57769/10 "2010-03-15T17:24:15Z")

</div>

I like Tony's final suggestion. In your base class initialize method, have it make a call to post\_initialize. All subclasses should then create a post\_initialize method if they need to do any construction (or leave it empty).

This technique is used in Eventmachine since its internals like to control when and how classes are instantiated.

cr

> **···**
>
> On Mar 15, 2010, at 12:07 PM, Tony Arcieri wrote:
> 
> > On Mon, Mar 15, 2010 at 7:41 AM, Andrea Dallera \<andrea@andreadallera.com\>wrote:
> > 
> > > Hei Chuck,
> > > 
> > > &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;that's exactly what i was trying to avoid.
> > 
> > One way to avoid it is to override new. You can use the "allocate" method  
> > to create a new object instance without invoking its constructor. Name the  
> > superclass's "initialize" method something different, like preinitialize,  
> > and invoke that yourself. Be sure to invoke initialize too, if it's  
> > defined.
> > 
> > I've used this approach in frameworks where I intend for users to subclass,  
> > but my general impression nowadays is I should use a lot cleaner base class  
> > that doesn't need these sorts of hax, or not expect users to ever define  
> > their own constructor.

---

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 15:11 UTC](https://rubytalk.org/t/overriding-new/57769/11 "2010-03-15T15:11:52Z")

</div>

I'm sorry, I looked before posting and i couldn't find anything. I'm  
looking now too and still I can't find it, so if you maybe have a  
pointer to that it would be really nice. Sorry for spamming.

> **···**
>
> --  
> Andrea Dallera
> 
> > **[GitHub - bolthar/freightrain: Ruby desktop development made easy](https://github.com/bolthar/freightrain)**
> >
> > Ruby desktop development made easy. Contribute to bolthar/freightrain development by creating an account on GitHub.
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog
> 
> On Tue, 2010-03-16 at 00:02 +0900, Aldric Giacomoni wrote:
> 
> > Chuck Remes wrote:  
> > \> On Mar 15, 2010, at 9:41 AM, Andrea Dallera wrote:  
> > \>  
> > \>\> Hei Chuck,  
> > \>\>  
> > \>\> that's exactly what i was trying to avoid. While I'm at it, let me be  
> > \>\> more specific about my problem, which is actually not just printing out  
> > \>\> text to the console but changing the state of the newly created  
> > \>\> instance:  
> > \>\>  
> > \>
> > 
> > Andrea:  
> > I think something similar was brought up on this mailing  
> > list/forum/newsgroup within the last two weeks or so. Take a look  
> > through the older topics.

---

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 18:48 UTC](https://rubytalk.org/t/overriding-new/57769/12 "2010-03-15T18:48:40Z")

</div>

Hei,

&nbsp;&nbsp;I am uncertain about what to do: on one side I'm very aware that it  
would be a huge hack and, before all, using this kind of "template  
method" in the base class, and having every element to inherit from it,  
is very unflexible. On the other side i've been using freightrain for  
quite a while now and i really really like the syntactic sugar, so  
things like  
MyFactory.getInstance() do  
&nbsp;&nbsp;# user defines their behavior here  
end  
as Walton (which i thank for the pointer) suggested are a big no no.

I like this way of doing it:  
def new(\*a,&b)  
&nbsp;&nbsp;obj = allocate  
&nbsp;&nbsp;#do your stuff  
&nbsp;&nbsp;obj.send(:initialize,\*a,&b)  
&nbsp;&nbsp;return obj  
end

What do you think about it? Aside from the performance hit (in my case i really don't case), are there any motivation i'm not seeing for not using it?  
Also forbidding to specify the constructor would be a way to go but i'd like to allow as much freedom as possible.

> **···**
>
> --  
> Andrea Dallera
> 
> > **[GitHub - bolthar/freightrain: Ruby desktop development made easy](https://github.com/bolthar/freightrain)**
> >
> > Ruby desktop development made easy. Contribute to bolthar/freightrain development by creating an account on GitHub.
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog
> 
> On Tue, 2010-03-16 at 02:24 +0900, Chuck Remes wrote:
> 
> > On Mar 15, 2010, at 12:07 PM, Tony Arcieri wrote:
> > 
> > \> On Mon, Mar 15, 2010 at 7:41 AM, Andrea Dallera \<andrea@andreadallera.com\>wrote:  
> > \>  
> > \>\> Hei Chuck,  
> > \>\>  
> > \>\> that's exactly what i was trying to avoid.  
> > \>  
> > \>  
> > \> One way to avoid it is to override new. You can use the "allocate" method  
> > \> to create a new object instance without invoking its constructor. Name the  
> > \> superclass's "initialize" method something different, like preinitialize,  
> > \> and invoke that yourself. Be sure to invoke initialize too, if it's  
> > \> defined.  
> > \>  
> > \> I've used this approach in frameworks where I intend for users to subclass,  
> > \> but my general impression nowadays is I should use a lot cleaner base class  
> > \> that doesn't need these sorts of hax, or not expect users to ever define  
> > \> their own constructor.
> > 
> > I like Tony's final suggestion. In your base class initialize method, have it make a call to post\_initialize. All subclasses should then create a post\_initialize method if they need to do any construction (or leave it empty).
> > 
> > This technique is used in Eventmachine since its internals like to control when and how classes are instantiated.
> > 
> > cr

---

<div class="post-metadata">

**Author:** ![Ken\_Bloom](https://avatars.discourse-cdn.com/v4/letter/k/f08c70/32.png) [@Ken\_Bloom](https://rubytalk.org/u/Ken_Bloom)\
**Post date:** [15 March 2010 19:08 UTC](https://rubytalk.org/t/overriding-new/57769/13 "2010-03-15T19:08:19Z")

</div>

> Hi everybody,
> 
> &nbsp;&nbsp;the whole issues comes from here:  
> [freightrain/lib/freightrain at master · bolthar/freightrain · GitHub](http://github.com/bolthar/freightrain/blob/master/lib/freightrain/)

freight\_view\_model.rb

> FreightViewModel is part of the framework, and if you're using it that's  
> the way you should do it:
> 
> class MyViewModel \< FreightViewModel
> 
> ...
> 
> end
> 
> what i don't like is that if you want to make \_your\_ viewmodel do stuff  
> on initialize, which is usual, you have to write your initialize method  
> as such:
> 
> def initialize  
> &nbsp;&nbsp;super  
> &nbsp;&nbsp;#your stuff here  
> end
> 
> otherwise the automagical initialization (like building views, hooking  
> to services, etc) doesn't work, because the constructor of  
> FreightViewModel (that is the one taking care of all this) doesn't get  
> called.  
> I know this is not extremely important (you just have to remind to call  
> super) but i'd prefer not to have that hassle : i forget it myself more  
> than often.

You ought to just get in the habit of remembering it.

Maybe you can write some kind of automatic checker that will look for  
definitions of initialize that don't call super.

I think it's always appropriate to call super in an initialize call,  
because everything descends from Object, and Object defines an initialize  
method.

--Ken

> **···**
>
> On Tue, 16 Mar 2010 00:04:59 +0900, Andrea Dallera wrote:
> 
> --  
> Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.  
> Department of Computer Science. Illinois Institute of Technology.  
> [http://www.iit.edu/~kbloom1/](http://www.iit.edu/~kbloom1/)

---

<div class="post-metadata">

**Author:** ![Andrea1](https://avatars.discourse-cdn.com/v4/letter/a/cdc98d/32.png) [@Andrea1](https://rubytalk.org/u/Andrea1)\
**Post date:** [20 March 2010 12:41 UTC](https://rubytalk.org/t/overriding-new/57769/14 "2010-03-20T12:41:19Z")

</div>

I suppose you could change a bit the design and use a hook method  
instead of initialize in the subclass. I mean, in the superclass you do  
all your automagical initalization, then you call a (blank) hook method,  
and later you redefine it when you build the new class. Something like  
this:

class Parent  
&nbsp;&nbsp;def initalize  
&nbsp;&nbsp;&nbsp;&nbsp;# do automagic stuff  
&nbsp;&nbsp;&nbsp;&nbsp;configure  
&nbsp;&nbsp;end

&nbsp;&nbsp;def configure  
&nbsp;&nbsp;&nbsp;&nbsp;# just a blank hook method  
&nbsp;&nbsp;end  
end

class Child \< Parent  
&nbsp;&nbsp;def configure  
&nbsp;&nbsp;&nbsp;&nbsp;# do some specific stuff  
&nbsp;&nbsp;end  
end

> **···**
>
> Andrea Dallera \<andrea@andreadallera.com\> wrote:
> 
> > what i don't like is that if you want to make \_your\_ viewmodel do stuff  
> > on initialize, which is usual, you have to write your initialize method  
> > as such:
> > 
> > def initialize  
> > &nbsp;&nbsp;super  
> > &nbsp;&nbsp;#your stuff here  
> > end
> 
> --  
> MySQL and PHP are popular not because of their quality, but despite it.

---

<div class="post-metadata">

**Author:** ![Walton\_Hoops1](https://avatars.discourse-cdn.com/v4/letter/w/77aa72/32.png) [@Walton\_Hoops1](https://rubytalk.org/u/Walton_Hoops1)\
**Post date:** [15 March 2010 16:33 UTC](https://rubytalk.org/t/overriding-new/57769/15 "2010-03-15T16:33:46Z")

</div>

Found it: [Is there a way to get a method to always run at the end of any descendent's initialize method? - Ruby - Ruby-Forum](http://www.ruby-forum.com/topic/204105)  
While it does offer some methods you might use, I highly recommend not  
trying to solve the problem this way. 'super' is an expected part of  
sub-classing, and there may be instances in which the sub-classer does  
\*not\* want your initializer to run. If this is something you need to  
do, I might be inclined to solve it with the factory approach. So  
instead those using your framework would do something like:  
MyFactory.getInstance() do  
# user defines their behavior here  
end

which returns an already initialized object.

> **···**
>
> On 3/15/2010 9:11 AM, Andrea Dallera wrote:
> 
> > I'm sorry, I looked before posting and i couldn't find anything. I'm  
> > looking now too and still I can't find it, so if you maybe have a  
> > pointer to that it would be really nice. Sorry for spamming.

---

<div class="post-metadata">

**Author:** ![Walton\_Hoops1](https://avatars.discourse-cdn.com/v4/letter/w/77aa72/32.png) [@Walton\_Hoops1](https://rubytalk.org/u/Walton_Hoops1)\
**Post date:** [15 March 2010 19:14 UTC](https://rubytalk.org/t/overriding-new/57769/16 "2010-03-15T19:14:33Z")

</div>

I assume that '#do your stuff' is where you do things like call the  
parents initializer?  
1) What happens is the programmer \*does\* call super in initialize.  
While sometimes it's ok for code to get run twice, sometimes it's not.  
Be sure that if you are ensuring the parent class's initialize method  
runs, that it doesn't foobar something if it runs twice because the user  
called 'super'.  
2) Are you sure there isn't an instance where someone would want to  
subclass your class, but not run the parents initializer? One example  
where I can think of this occurring is doing mocks for unit testing. I  
may still want to use some of the functionality from your class (thus  
subclassing it), but cut out some of the backing guts and replace them  
with something I have control over.

Provided you have thought about those two things, and still think this  
is the right choice, then I see no problem with this code.

> **···**
>
> On 3/15/2010 12:48 PM, Andrea Dallera wrote:
> 
> > Hei,
> > 
> > &nbsp;&nbsp;I am uncertain about what to do: on one side I'm very aware that it  
> > would be a huge hack and, before all, using this kind of "template  
> > method" in the base class, and having every element to inherit from it,  
> > is very unflexible. On the other side i've been using freightrain for  
> > quite a while now and i really really like the syntactic sugar, so  
> > things like  
> > MyFactory.getInstance() do  
> > &nbsp;&nbsp;# user defines their behavior here  
> > end  
> > as Walton (which i thank for the pointer) suggested are a big no no.
> > 
> > I like this way of doing it:  
> > def new(\*a,&b)  
> > &nbsp;&nbsp;obj = allocate  
> > &nbsp;&nbsp;#do your stuff  
> > &nbsp;&nbsp;obj.send(:initialize,\*a,&b)  
> > &nbsp;&nbsp;return obj  
> > end
> > 
> > What do you think about it? Aside from the performance hit (in my case i really don't case), are there any motivation i'm not seeing for not using it?  
> > Also forbidding to specify the constructor would be a way to go but i'd like to allow as much freedom as possible.

---

<div class="post-metadata">

**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\
**Post date:** [15 March 2010 16:42 UTC](https://rubytalk.org/t/overriding-new/57769/17 "2010-03-15T16:42:29Z")

</div>

I agree: calling super is the default method for making sure super  
classes are initialized properly. I would stick to that rather than  
inventing some magic behind the scenes. For exampl, if you override  
#new to do what OP wants (which is possible) measures should be taken  
to not break if someone actually invokes super in their #initialize.

Kind regards

robert

> **···**
>
> 2010/3/15 Walton Hoops \<walton@vyper.hopto.org\>:
> 
> > On 3/15/2010 9:11 AM, Andrea Dallera wrote:
> > 
> > > I'm sorry, I looked before posting and i couldn't find anything. I'm  
> > > looking now too and still I can't find it, so if you maybe have a  
> > > pointer to that it would be really nice. Sorry for spamming.
> > 
> > Found it: [Is there a way to get a method to always run at the end of any descendent's initialize method? - Ruby - Ruby-Forum](http://www.ruby-forum.com/topic/204105)  
> > While it does offer some methods you might use, I highly recommend not  
> > trying to solve the problem this way. 'super' is an expected part of  
> > sub-classing, and there may be instances in which the sub-classer does  
> > \*not\* want your initializer to run. If this is something you need to  
> > do, I might be inclined to solve it with the factory approach. So  
> > instead those using your framework would do something like:  
> > MyFactory.getInstance() do  
> > # user defines their behavior here  
> > end
> > 
> > which returns an already initialized object.
> 
> --  
> remember.guy do |as, often| as.you\_can - without end  
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)

---

<div class="post-metadata">

**Author:** ![Andrea\_Dallera](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Andrea\_Dallera](https://rubytalk.org/u/Andrea_Dallera)\
**Post date:** [15 March 2010 20:46 UTC](https://rubytalk.org/t/overriding-new/57769/18 "2010-03-15T20:46:08Z")

</div>

I should have been clearer in the example. This is the actual situation:

class FreightViewModel

&nbsp;&nbsp;def initialize  
&nbsp;&nbsp;&nbsp;&nbsp;do\_some\_init\_stuff()  
&nbsp;&nbsp;end

end

and this is what it will become if i apply that solution:

class FreightViewModel

&nbsp;&nbsp;def new(\*args, &block)  
&nbsp;&nbsp;&nbsp;&nbsp;obj = allocate  
&nbsp;&nbsp;&nbsp;&nbsp;obj.do\_some\_init\_stuff  
&nbsp;&nbsp;&nbsp;&nbsp;obj.send(:initialize, \*args, &block)  
&nbsp;&nbsp;&nbsp;&nbsp;return obj  
&nbsp;&nbsp;end

end

> What happens is the programmer \*does\* call super in initialize.  
> While sometimes it's ok for code to get run twice, sometimes it's not.  
> Be sure that if you are ensuring the parent class's initialize method  
> runs, that it doesn't foobar something if it runs twice because the user  
> called 'super'.

Calling super shouldn't be a problem in this case: the constructor of the base class does nothing...right?

> Are you sure there isn't an instance where someone would want to  
> subclass your class, but not run the parents initializer? One example  
> where I can think of this occurring is doing mocks for unit testing. I  
> may still want to use some of the functionality from your class (thus  
> subclassing it), but cut out some of the backing guts and replace them  
> with something I have control over.

Good point. I'm taking care of this, in a way that provides a full stub  
(with all the dependencies stubbed and injected) for integration testing  
with one line of code, which was one of the initial objectives: i come  
from WPF and it can be a pain to write integration testing for a VM with  
even just 3 services, i wanted to be able to test without having to  
write huge and complex setups all the time. Still, one can think of  
other cases where a VM is is still needed "uninitialized": i guess i'll  
provide an hard switch if the case actually arises.

Thanks a lot for all the suggestions!

> **···**
>
> --  
> Andrea Dallera
> 
> > **[GitHub - bolthar/freightrain: Ruby desktop development made easy](https://github.com/bolthar/freightrain)**
> >
> > Ruby desktop development made easy. Contribute to bolthar/freightrain development by creating an account on GitHub.
> 
> > **[using (IMHO)](https://usingimho.wordpress.com/)**
> >
> > Andrea Dallera 's blog
> 
> On Tue, 2010-03-16 at 04:14 +0900, Walton Hoops wrote:
> 
> > On 3/15/2010 12:48 PM, Andrea Dallera wrote:  
> > \> Hei,  
> > \>  
> > \> I am uncertain about what to do: on one side I'm very aware that it  
> > \> would be a huge hack and, before all, using this kind of "template  
> > \> method" in the base class, and having every element to inherit from it,  
> > \> is very unflexible. On the other side i've been using freightrain for  
> > \> quite a while now and i really really like the syntactic sugar, so  
> > \> things like  
> > \> MyFactory.getInstance() do  
> > \> # user defines their behavior here  
> > \> end  
> > \> as Walton (which i thank for the pointer) suggested are a big no no.  
> > \>  
> > \> I like this way of doing it:  
> > \> def new(\*a,&b)  
> > \> obj = allocate  
> > \> #do your stuff  
> > \> obj.send(:initialize,\*a,&b)  
> > \> return obj  
> > \> end  
> > \>  
> > \> What do you think about it? Aside from the performance hit (in my case i really don't case), are there any motivation i'm not seeing for not using it?  
> > \> Also forbidding to specify the constructor would be a way to go but i'd like to allow as much freedom as possible.  
> > \>  
> > \>  
> > I assume that '#do your stuff' is where you do things like call the  
> > parents initializer?  
> > 1) What happens is the programmer \*does\* call super in initialize.  
> > While sometimes it's ok for code to get run twice, sometimes it's not.  
> > Be sure that if you are ensuring the parent class's initialize method  
> > runs, that it doesn't foobar something if it runs twice because the user  
> > called 'super'.  
> > 2) Are you sure there isn't an instance where someone would want to  
> > subclass your class, but not run the parents initializer? One example  
> > where I can think of this occurring is doing mocks for unit testing. I  
> > may still want to use some of the functionality from your class (thus  
> > subclassing it), but cut out some of the backing guts and replace them  
> > with something I have control over.
> > 
> > Provided you have thought about those two things, and still think this  
> > is the right choice, then I see no problem with this code.

---

<div class="post-metadata">

**Author:** ![Walton\_Hoops1](https://avatars.discourse-cdn.com/v4/letter/w/77aa72/32.png) [@Walton\_Hoops1](https://rubytalk.org/u/Walton_Hoops1)\
**Post date:** [15 March 2010 21:18 UTC](https://rubytalk.org/t/overriding-new/57769/19 "2010-03-15T21:18:04Z")

</div>

> I should have been clearer in the example. This is the actual situation:
> 
> class FreightViewModel
> 
> &nbsp;&nbsp;def initialize  
> &nbsp;&nbsp;&nbsp;&nbsp;do\_some\_init\_stuff()  
> &nbsp;&nbsp;end
> 
> end
> 
> and this is what it will become if i apply that solution:
> 
> class FreightViewModel
> 
> &nbsp;&nbsp;def new(\*args, &block)  
> &nbsp;&nbsp;&nbsp;&nbsp;obj = allocate  
> &nbsp;&nbsp;&nbsp;&nbsp;obj.do\_some\_init\_stuff  
> &nbsp;&nbsp;&nbsp;&nbsp;obj.send(:initialize, \*args, &block)  
> &nbsp;&nbsp;&nbsp;&nbsp;return obj  
> &nbsp;&nbsp;end
> 
> end
> 
> > What happens is the programmer \*does\* call super in initialize.  
> > While sometimes it's ok for code to get run twice, sometimes it's not.  
> > Be sure that if you are ensuring the parent class's initialize method  
> > runs, that it doesn't foobar something if it runs twice because the user  
> > called 'super'.  
> > &nbsp;&nbsp;&nbsp;&nbsp;
> 
> Calling super shouldn't be a problem in this case: the constructor of the base class does nothing...right?  
> &nbsp;&nbsp;

Right, so not an issue in this case.

> > Are you sure there isn't an instance where someone would want to  
> > subclass your class, but not run the parents initializer? One example  
> > where I can think of this occurring is doing mocks for unit testing. I  
> > may still want to use some of the functionality from your class (thus  
> > subclassing it), but cut out some of the backing guts and replace them  
> > with something I have control over.  
> > &nbsp;&nbsp;&nbsp;&nbsp;
> 
> Good point. I'm taking care of this, in a way that provides a full stub  
> (with all the dependencies stubbed and injected) for integration testing  
> with one line of code, which was one of the initial objectives: i come  
> from WPF and it can be a pain to write integration testing for a VM with  
> even just 3 services, i wanted to be able to test without having to  
> write huge and complex setups all the time. Still, one can think of  
> other cases where a VM is is still needed "uninitialized": i guess i'll  
> provide an hard switch if the case actually arises.
> 
> Thanks a lot for all the suggestions!  
> &nbsp;&nbsp;

Sounds to me like you've given it plenty of thought and are good to go.  
Best of luck with your project!

> **···**
>
> On 3/15/2010 2:46 PM, Andrea Dallera wrote: