Rails spinoffs - Jun 2006 - Implementing a boolean "switch" in a Class

I need a single boolean which would be "globally" accessible to all
instances of a class.  Seems like the boolean should be in the class
prototype, but I was troubled by the difficulty of setting the prototype
boolean to true.  Maybe I''m missing something?
 
var MyObject = Class.create();
 
MyObject.prototype = {
 bSwitch: false,
 ... other methods and properties
}
 
var oMyOb1 = new MyObject();
var oMyOb2 = new MyObject();
alert(oMyOb1.bSwitch); // reports false 
alert(oMyOb2.bSwitch); // reports false
 
Now set the value of bSwitch to true so all the oMyObN''s will see a
true
value.
 
I can see the following methods...
 
// __proto__ works in Firefox/Safari but isn''t available in IE...
oMyOb1.__proto__.bSwitch = true; 
alert(oMyOb1.bSwitch); // reports true 
alert(oMyOb2.bSwitch); // reports true
 
// This changes bSwitch for a single instance.  Not in the prototype.
oMyOb1.bSwitch = true;
alert(oMyOb1.bSwitch); // reports true 
alert(oMyOb2.bSwitch); // reports false, not what we want.
 
// Seems strange to me to reference the Class, but this works...
MyObject.prototype.bSwitch = true; 
alert(oMyOb1.bSwitch); // reports true 
alert(oMyOb2.bSwitch); // reports true
 
// It''s a little more satisfying to create a method to hide this
reference
to the class...
MyObject.prototype = {
 bSwitch: false,
 setSwitch: function() {MyObject.prototype.bSwitch = true;} 
}
// Now this works, and only requires a reference to a method on an instance 
oMyOb1.setSwitch(); 
alert(oMyOb1.bSwitch); // reports true 
alert(oMyOb2.bSwitch); // reports true
 
// I thought all objects had prototypes.  Why doesn''t this work?
oMyOb1.prototype.bSwitch = true;  // error:  oMyOb1 is not a function
 
Is there another method that I''ve missed?  Did prototype.js extend
__proto__
to work in IE?
 
Sam
 


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I''ve always though the ptototype objects are not mutable after
instances have been made. I.e. changes to prototypes will not update
existing instances.

I''ve always done this:

Object.extend(MyObject, {bSwitch: false});

then MyObjec.bSwitch can be set/got globally


On 21/06/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
>
> I need a single boolean which would be "globally" accessible to
all
> instances of a class.  Seems like the boolean should be in the class
> prototype, but I was troubled by the difficulty of setting the prototype
> boolean to true.  Maybe I''m missing something?
>
> var MyObject = Class.create();
>
> MyObject.prototype = {
>  bSwitch: false,
>  ... other methods and properties
> }
>
> var oMyOb1 = new MyObject();
> var oMyOb2 = new MyObject();
> alert(oMyOb1.bSwitch); // reports false
> alert(oMyOb2.bSwitch); // reports false
>
> Now set the value of bSwitch to true so all the oMyObN''s will see
a true
> value.
>
> I can see the following methods...
>
> // __proto__ works in Firefox/Safari but isn''t available in IE...
> oMyOb1.__proto__.bSwitch = true;
>
> alert(oMyOb1.bSwitch); // reports true
> alert(oMyOb2.bSwitch); // reports true
>
> // This changes bSwitch for a single instance.  Not in the prototype.
> oMyOb1.bSwitch = true;
>
> alert(oMyOb1.bSwitch); // reports true
> alert(oMyOb2.bSwitch); // reports false, not what we want.
>
> // Seems strange to me to reference the Class, but this works...
> MyObject.prototype.bSwitch = true;
> alert(oMyOb1.bSwitch); // reports true
> alert(oMyOb2.bSwitch); // reports true
>
> // It''s a little more satisfying to create a method to hide this
reference
> to the class...
>
> MyObject.prototype = {
>  bSwitch: false,
>  setSwitch: function() {MyObject.prototype.bSwitch = true;}
> }
> // Now this works, and only requires a reference to a method on an instance
> oMyOb1.setSwitch();
>
> alert(oMyOb1.bSwitch); // reports true
> alert(oMyOb2.bSwitch); // reports true
>
>
> // I thought all objects had prototypes.  Why doesn''t this work?
> oMyOb1.prototype.bSwitch = true;  // error:  oMyOb1 is not a function
>  Is there another method that I''ve missed?  Did prototype.js
extend
> __proto__ to work in IE?
>
> Sam
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

-- 
Andrew Tetlaw
htp://tetlaw.id.au

Nope... in fact this is one of the "dynamic" benefits of a prototype
based
object system.  Changing the prototype of the "class" function (the
function
from which the other references are constructed), changes the state of all
instances automatically.

MyObject.prototype.bSwitch = true; is the correct way to achieve what you
are looking for. Why would you want to do this by using an instance of said
class? It seems to me you''d _want_ to _not_ have to know what instances
are
floating around in your application, so the "class"
function''s prototype is
the natural place to make this change. In other words, you have 10 widgets
and a couple of flibbets, maybe a few woozles on your page, each of them
possibly containing N instances of MyObject. Why would you want to have to
know the name of one of those instances to set this switch across all of
them... see my point?

On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> I''ve always though the ptototype objects are not mutable after
> instances have been made. I.e. changes to prototypes will not update
> existing instances.
>
> I''ve always done this:
>
> Object.extend(MyObject, {bSwitch: false});
>
> then MyObjec.bSwitch can be set/got globally
>
>
> On 21/06/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
> >
> >
> > I need a single boolean which would be "globally" accessible
to all
> > instances of a class.  Seems like the boolean should be in the class
> > prototype, but I was troubled by the difficulty of setting the
prototype
> > boolean to true.  Maybe I''m missing something?
> >
> > var MyObject = Class.create();
> >
> > MyObject.prototype = {
> >  bSwitch: false,
> >  ... other methods and properties
> > }
> >
> > var oMyOb1 = new MyObject();
> > var oMyOb2 = new MyObject();
> > alert(oMyOb1.bSwitch); // reports false
> > alert(oMyOb2.bSwitch); // reports false
> >
> > Now set the value of bSwitch to true so all the oMyObN''s will
see a true
> > value.
> >
> > I can see the following methods...
> >
> > // __proto__ works in Firefox/Safari but isn''t available in
IE...
> > oMyOb1.__proto__.bSwitch = true;
> >
> > alert(oMyOb1.bSwitch); // reports true
> > alert(oMyOb2.bSwitch); // reports true
> >
> > // This changes bSwitch for a single instance.  Not in the prototype.
> > oMyOb1.bSwitch = true;
> >
> > alert(oMyOb1.bSwitch); // reports true
> > alert(oMyOb2.bSwitch); // reports false, not what we want.
> >
> > // Seems strange to me to reference the Class, but this works...
> > MyObject.prototype.bSwitch = true;
> > alert(oMyOb1.bSwitch); // reports true
> > alert(oMyOb2.bSwitch); // reports true
> >
> > // It''s a little more satisfying to create a method to hide
this
> reference
> > to the class...
> >
> > MyObject.prototype = {
> >  bSwitch: false,
> >  setSwitch: function() {MyObject.prototype.bSwitch = true;}
> > }
> > // Now this works, and only requires a reference to a method on an
> instance
> > oMyOb1.setSwitch();
> >
> > alert(oMyOb1.bSwitch); // reports true
> > alert(oMyOb2.bSwitch); // reports true
> >
> >
> > // I thought all objects had prototypes.  Why doesn''t this
work?
> > oMyOb1.prototype.bSwitch = true;  // error:  oMyOb1 is not a function
> >  Is there another method that I''ve missed?  Did prototype.js
extend
> > __proto__ to work in IE?
> >
> > Sam
> >
> > _______________________________________________
> > Rails-spinoffs mailing list
> > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> >
> >
> >
>
>
> --
> Andrew Tetlaw
> htp://tetlaw.id.au
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>

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Nope... in fact this is one of the "dynamic" benefits of a prototype
based
object system.  Changing the prototype of the "class" function (the
function
from which the other references are constructed), changes the state of all
instances automatically. 

MyObject.prototype.bSwitch = true; is the correct way to achieve what you
are looking for. Why would you want to do this by using an instance of said
class? It seems to me you''d _want_ to _not_ have to know what instances
are
floating around in your application, so the "class"
function''s prototype is
the natural place to make this change. In other words, you have 10 widgets
and a couple of flibbets, maybe a few woozles on your page, each of them
possibly containing N instances of MyObject. Why would you want to have to
know the name of one of those instances to set this switch across all of
them... see my point? 


After declaring the Class, I''ve never had to mess with a class before. 
This
takes some getting used to, and it seems strange that I can''t reference
the
class / constructor from an instance without knowing the constructor''s
name???
 
I was under a mistaken assumption that
 
oMyObj1.prototype
 
would move up the prototype chain to reach the constructor function
MyObject. 
 
If
 
var oMyObj5 = new MyObject();
 
doesn''t it make sense that there should be a pointer on the oMyObj5
object
which points back to the constructor function?  Without __proto__,
there''s
no way to reach back to the constructor without knowing the
constructor''s
name?
 
Sam
 


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But, how can you create an instance of a class without knowing the
constructor''s name? It''s much more likely you know the
constructor''s name
than the name of any given instance.

But, try this... (not sure if its works but worth a shot if you need it)...

oMyObj5.constructor.prototype.bSwitch = true;

On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
> Nope... in fact this is one of the "dynamic" benefits of a
prototype based
> object system.  Changing the prototype of the "class" function
(the function
> from which the other references are constructed), changes the state of all
> instances automatically.
>
> MyObject.prototype.bSwitch = true; is the correct way to achieve what you
> are looking for. Why would you want to do this by using an instance of said
> class? It seems to me you''d _want_ to _not_ have to know what
instances are
> floating around in your application, so the "class"
function''s prototype is
> the natural place to make this change. In other words, you have 10 widgets
> and a couple of flibbets, maybe a few woozles on your page, each of them
> possibly containing N instances of MyObject. Why would you want to have to
> know the name of one of those instances to set this switch across all of
> them... see my point?
>
> After declaring the Class, I''ve never had to mess with a class
before.
> This takes some getting used to, and it seems strange that I can''t
reference
> the class / constructor from an instance without knowing the
constructor''s
> name???
>
> I was under a mistaken assumption that
>
> oMyObj1.prototype
>
> would move up the prototype chain to reach the constructor function
> MyObject.
>
> If
>
> var oMyObj5 = new MyObject();
>
> doesn''t it make sense that there should be a pointer on the
oMyObj5 object
> which points back to the constructor function?  Without __proto__,
there''s
> no way to reach back to the constructor without knowing the
constructor''s
> name?
>
> Sam
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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Also... you said:

** After declaring the Class, I''ve never had to mess with a class
before.

:-) you''re still thinking of javascript as a classical OO language,
when
it''s not. Embrace the power of the prototype.

On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
> Nope... in fact this is one of the "dynamic" benefits of a
prototype based
> object system.  Changing the prototype of the "class" function
(the function
> from which the other references are constructed), changes the state of all
> instances automatically.
>
> MyObject.prototype.bSwitch = true; is the correct way to achieve what you
> are looking for. Why would you want to do this by using an instance of said
> class? It seems to me you''d _want_ to _not_ have to know what
instances are
> floating around in your application, so the "class"
function''s prototype is
> the natural place to make this change. In other words, you have 10 widgets
> and a couple of flibbets, maybe a few woozles on your page, each of them
> possibly containing N instances of MyObject. Why would you want to have to
> know the name of one of those instances to set this switch across all of
> them... see my point?
>
> After declaring the Class, I''ve never had to mess with a class
before.
> This takes some getting used to, and it seems strange that I can''t
reference
> the class / constructor from an instance without knowing the
constructor''s
> name???
>
> I was under a mistaken assumption that
>
> oMyObj1.prototype
>
> would move up the prototype chain to reach the constructor function
> MyObject.
>
> If
>
> var oMyObj5 = new MyObject();
>
> doesn''t it make sense that there should be a pointer on the
oMyObj5 object
> which points back to the constructor function?  Without __proto__,
there''s
> no way to reach back to the constructor without knowing the
constructor''s
> name?
>
> Sam
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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yea.. the constructor thing I posted probably doesn''t exist... I just
thought I remembered seeing that somewhere...

On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> But, how can you create an instance of a class without knowing the
> constructor''s name? It''s much more likely you know the
constructor''s name
> than the name of any given instance.
>
> But, try this... (not sure if its works but worth a shot if you need
> it)...
>
> oMyObj5.constructor.prototype.bSwitch = true;
>
> On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
> > Nope... in fact this is one of the "dynamic" benefits of a
prototype
> > based object system.  Changing the prototype of the "class"
function (the
> > function from which the other references are constructed), changes the
state
> > of all instances automatically.
> >
> > MyObject.prototype.bSwitch = true; is the correct way to achieve what
> > you are looking for. Why would you want to do this by using an
instance of
> > said class? It seems to me you''d _want_ to _not_ have to know
what instances
> > are floating around in your application, so the "class"
function''s prototype
> > is the natural place to make this change. In other words, you have 10
> > widgets and a couple of flibbets, maybe a few woozles on your page,
each of
> > them possibly containing N instances of MyObject. Why would you want
to have
> > to know the name of one of those instances to set this switch across
all of
> > them... see my point?
> >
> > After declaring the Class, I''ve never had to mess with a
class before.
> > This takes some getting used to, and it seems strange that I
can''t reference
> > the class / constructor from an instance without knowing the
constructor''s
> > name???
> >
> > I was under a mistaken assumption that
> >
> > oMyObj1.prototype
> >
> > would move up the prototype chain to reach the constructor function
> > MyObject.
> >
> > If
> >
> > var oMyObj5 = new MyObject();
> >
> > doesn''t it make sense that there should be a pointer on the
oMyObj5
> > object which points back to the constructor function?  Without
__proto__,
> > there''s no way to reach back to the constructor without
knowing the
> > constructor''s name?
> >
> > Sam
> >
> >
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>
>

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Also... you said:

** After declaring the Class, I''ve never had to mess with a class
before.

:-) you''re still thinking of javascript as a classical OO language,
when
it''s not. Embrace the power of the prototype.

Yes, my problem is getting to the point where this "feels" right.  
 
oMyObject.constructor.prototype.bSwitch = true; // doesn''t produce an
error,
and doesn''t change the global value in the class prototype, so what is
it
changing?
 
<script type="text/javascript">
var test = function () {}
test.prototype = {color: ''red''};
var oTest1 = new test();
var oTest2 = new test();
oTest2.__proto__.color = ''blue'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color); //
blue blue
test.prototype.color = ''green'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color); //
green green
oTest1.constructor.prototype.color = ''purple'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color); //
green green -- not what we want
</script>
 



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Hmm, interesting. Frankly, i have no idea about the constructor thing --
half expected it to throw an error. But I''m still not sure why
you''re so
reluctanct to use the main prototype; this is what it''s for.
Ultimately,
you''re looking for a way to use an instance to _get_at_ the main
prototype... so why not just do it directly? It''s a feature of the
language,
man.

test.prototype.color = ''purple'';

On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
>  Also... you said:
>
> ** After declaring the Class, I''ve never had to mess with a class
before.
>
> :-) you''re still thinking of javascript as a classical OO
language, when
> it''s not. Embrace the power of the prototype.
>
> Yes, my problem is getting to the point where this "feels" right.
>
> oMyObject.constructor.prototype.bSwitch = true; // doesn''t produce
an
> error, and doesn''t change the global value in the class prototype,
so what
> is it changing?
>
> <script type="text/javascript">
> var test = function () {}
> test.prototype = {color: ''red''};
> var oTest1 = new test();
> var oTest2 = new test();
> oTest2.__proto__.color = ''blue'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
> // blue blue
> test.prototype.color = ''green'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
> // green green
> oTest1.constructor.prototype.color = ''purple'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
> // green green -- not what we want
> </script>
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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Hmm, interesting. Frankly, i have no idea about the constructor thing --
half expected it to throw an error. But I''m still not sure why
you''re so
reluctanct to use the main prototype; this is what it''s for.
Ultimately,
you''re looking for a way to use an instance to _get_at_ the main
prototype... so why not just do it directly? It''s a feature of the
language,
man. 

test.prototype.color = ''purple'';
 
I believe you are right.  It took a little getting used to, so no problem,
and I''m glad to have had some confirmation of that approach in this
thread.
 
So... what does oMyInstance.contructor point to and how would I find out?
;-)
 
 



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Not sure... but i''d start by inspecting it, using various different
"classes"...

for (var p in oMyInstance.constructor)
{
alert("p = " + oMyInstance[p]);
}

On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
>  Hmm, interesting. Frankly, i have no idea about the constructor thing --
> half expected it to throw an error. But I''m still not sure why
you''re so
> reluctanct to use the main prototype; this is what it''s for.
Ultimately,
> you''re looking for a way to use an instance to _get_at_ the main
> prototype... so why not just do it directly? It''s a feature of the
language,
> man.
>
> test.prototype.color = ''purple'';
>
> I believe you are right.  It took a little getting used to, so no problem,
> and I''m glad to have had some confirmation of that approach in
this thread.
>
> So... what does oMyInstance.contructor point to and how would I find out?
> ;-)
>
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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typo...

alert("p = " + oMyInstance.constructor[p]);

On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> Not sure... but i''d start by inspecting it, using various
different
> "classes"...
>
> for (var p in oMyInstance.constructor)
> {
> alert("p = " + oMyInstance[p]);
> }
>
> On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
> >  Hmm, interesting. Frankly, i have no idea about the constructor thing
> > -- half expected it to throw an error. But I''m still not sure
why you''re so
> > reluctanct to use the main prototype; this is what it''s for.
Ultimately,
> > you''re looking for a way to use an instance to _get_at_ the
main
> > prototype... so why not just do it directly? It''s a feature
of the language,
> > man.
> >
> > test.prototype.color = ''purple'';
> >
> > I believe you are right.  It took a little getting used to, so no
> > problem, and I''m glad to have had some confirmation of that
approach in this
> > thread.
> >
> > So... what does oMyInstance.contructor point to and how would I find
> > out?  ;-)
> >
> >
> >
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>
>

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This may also help,
http://lxr.mozilla.org/seamonkey/source/js/src/README.html

On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> typo...
>
> alert("p = " + oMyInstance.constructor[p]);
>
> On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> wrote:
>
> > Not sure... but i''d start by inspecting it, using various
different
> > "classes"...
> >
> > for (var p in oMyInstance.constructor)
> > {
> > alert("p = " + oMyInstance[p]);
> > }
> >
> > On 6/21/06, Sam <
sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org> wrote:
> >
> > >  Hmm, interesting. Frankly, i have no idea about the constructor
thing
> > > -- half expected it to throw an error. But I''m still not
sure why you''re so
> > > reluctanct to use the main prototype; this is what it''s
for. Ultimately,
> > > you''re looking for a way to use an instance to _get_at_
the main
> > > prototype... so why not just do it directly? It''s a
feature of the language,
> > > man.
> > >
> > > test.prototype.color = ''purple'';
> > >
> > > I believe you are right.  It took a little getting used to, so no
> > > problem, and I''m glad to have had some confirmation of
that approach in this
> > > thread.
> > >
> > > So... what does oMyInstance.contructor point to and how would I
find
> > > out?  ;-)
> > >
> > >
> > >
> >
> > _______________________________________________
> > Rails-spinoffs mailing list
> > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> >
> >
> >
> >
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

-- 
Jesse Kuhnert
Tacos/Tapestry, team member/developer

Open source based consulting work centered around
dojo/tapestry/tacos/hivemind.


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oops, caught another typo...

alert(p + " = " + oMyInstance.constructor[p]);

On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> typo...
>
> alert("p = " + oMyInstance.constructor[p]);
>
> On 6/21/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> wrote:
>
> > Not sure... but i''d start by inspecting it, using various
different
> > "classes"...
> >
> > for (var p in oMyInstance.constructor)
> > {
> > alert("p = " + oMyInstance[p]);
> > }
> >
> > On 6/21/06, Sam <
sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org> wrote:
> >
> > >  Hmm, interesting. Frankly, i have no idea about the constructor
thing
> > > -- half expected it to throw an error. But I''m still not
sure why you''re so
> > > reluctanct to use the main prototype; this is what it''s
for. Ultimately,
> > > you''re looking for a way to use an instance to _get_at_
the main
> > > prototype... so why not just do it directly? It''s a
feature of the language,
> > > man.
> > >
> > > test.prototype.color = ''purple'';
> > >
> > > I believe you are right.  It took a little getting used to, so no
> > > problem, and I''m glad to have had some confirmation of
that approach in this
> > > thread.
> > >
> > > So... what does oMyInstance.contructor point to and how would I
find
> > > out?  ;-)
> > >
> > >
> > >
> >
> > _______________________________________________
> > Rails-spinoffs mailing list
> > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> >
> >
> >
> >
>

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Not sure... but i''d start by inspecting it, using various different
"classes"...

for (var p in oMyInstance.constructor)
{

alert("p = " + oMyInstance[p]);

}


 Seems to point to nothing in Firefox anyway, the only property returned is:
color=''purple'';
 
<script type="text/javascript">
var test = function () {}
test.prototype = {color: ''red''};
var oTest1 = new test();
var oTest2 = new test();
oTest2.__proto__.color = ''blue'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
test.prototype.color = ''green'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
oTest1.constructor.prototype.color = ''purple'';
alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
 

for (var p in oTest1.constructor) {
 alert(p + " = " + oTest1.constructor[p]); // color=purple
}
 


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Very interesting. It would seem the constructor points to a floating
instance, not the actual prototype.

I wonder what these 3 variations do...

oTest1.constructor.color = ''purple'';
oTest1.constructor.constructor.color = ''purple'';
oTest1.constructor.constructor.prototype.color = ''purple'';

On 6/21/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
>
>  Not sure... but i''d start by inspecting it, using various
different
> "classes"...
>
> for (var p in oMyInstance.constructor)
> {
> alert("p = " + oMyInstance[p]);
> }
>
>  Seems to point to nothing in Firefox anyway, the only property returned
> is:  color=''purple'';
>
> <script type="text/javascript">
> var test = function () {}
> test.prototype = {color: ''red''};
> var oTest1 = new test();
> var oTest2 = new test();
> oTest2.__proto__.color = ''blue'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
> test.prototype.color = ''green'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
> oTest1.constructor.prototype.color = ''purple'';
> alert(''oTest1:color='' + oTest1.color + ''
oTest2:color='' + oTest2.color);
>
>
> for (var p in oTest1.constructor) {
>  alert(p + " = " + oTest1.constructor[p]); // color=purple
> }
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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On 21/06/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Nope... in fact this is one of the "dynamic" benefits of a
prototype based
> object system.  Changing the prototype of the "class" function
(the function
> from which the other references are constructed), changes the state of all
> instances automatically.
>
> MyObject.prototype.bSwitch = true; is the correct way to achieve what you
> are looking for. Why would you want to do this by using an instance of said
> class? It seems to me you''d _want_ to _not_ have to know what
instances are
> floating around in your application, so the "class"
function''s prototype is
> the natural place to make this change. In other words, you have 10 widgets
> and a couple of flibbets, maybe a few woozles on your page, each of them
> possibly containing N instances of MyObject. Why would you want to have to
> know the name of one of those instances to set this switch across all of
> them... see my point?
Actually by MyObjec.bSwitch I was not refering to an instance but the
the constructor. i.e. it''s a Class or Static member of the global
MyObject object.

The constructor of a class is an object too and can be referenced and
have members

You can still say

var MyObject = Class.create();
MyObject.prototype = {
 ... other methods and properties
}
MyObject.bSwitch = false;

obj1 = new MyObject();
obj2 = new MyObject();

But MyObject.bSwitch will be global.

>
> On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > I''ve always though the ptototype objects are not mutable
after
> > instances have been made. I.e. changes to prototypes will not update
> > existing instances.
> >
> > I''ve always done this:
> >
> > Object.extend(MyObject, {bSwitch: false});
> >
> > then MyObjec.bSwitch can be set/got globally
> >
> >
> > On 21/06/06, Sam
<sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org> wrote:
> > >
> > >
> > > I need a single boolean which would be "globally"
accessible to all
> > > instances of a class.  Seems like the boolean should be in the
class
> > > prototype, but I was troubled by the difficulty of setting the
prototype
> > > boolean to true.  Maybe I''m missing something?
> > >
> > > var MyObject = Class.create();
> > >
> > > MyObject.prototype = {
> > >  bSwitch: false,
> > >  ... other methods and properties
> > > }
> > >
> > > var oMyOb1 = new MyObject();
> > > var oMyOb2 = new MyObject();
> > > alert(oMyOb1.bSwitch); // reports false
> > > alert(oMyOb2.bSwitch); // reports false
> > >
> > > Now set the value of bSwitch to true so all the oMyObN''s
will see a true
> > > value.
> > >
> > > I can see the following methods...
> > >
> > > // __proto__ works in Firefox/Safari but isn''t available
in IE...
> > > oMyOb1.__proto__.bSwitch = true;
> > >
> > > alert(oMyOb1.bSwitch); // reports true
> > > alert(oMyOb2.bSwitch); // reports true
> > >
> > > // This changes bSwitch for a single instance.  Not in the
prototype.
> > > oMyOb1.bSwitch = true;
> > >
> > > alert(oMyOb1.bSwitch); // reports true
> > > alert(oMyOb2.bSwitch); // reports false, not what we want.
> > >
> > > // Seems strange to me to reference the Class, but this works...
> > > MyObject.prototype.bSwitch = true;
> > > alert(oMyOb1.bSwitch); // reports true
> > > alert(oMyOb2.bSwitch); // reports true
> > >
> > > // It''s a little more satisfying to create a method to
hide this
> reference
> > > to the class...
> > >
> > > MyObject.prototype = {
> > >  bSwitch: false,
> > >  setSwitch: function() {MyObject.prototype.bSwitch = true;}
> > > }
> > > // Now this works, and only requires a reference to a method on
an
> instance
> > > oMyOb1.setSwitch();
> > >
> > > alert(oMyOb1.bSwitch); // reports true
> > > alert(oMyOb2.bSwitch); // reports true
> > >
> > >
> > > // I thought all objects had prototypes.  Why doesn''t
this work?
> > > oMyOb1.prototype.bSwitch = true;  // error:  oMyOb1 is not a
function
> > >  Is there another method that I''ve missed?  Did
prototype.js extend
> > > __proto__ to work in IE?
> > >
> > > Sam
> > >
> > > _______________________________________________
> > > Rails-spinoffs mailing list
> > > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > >
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> > >
> > >
> > >
> >
> >
> > --
> > Andrew Tetlaw
> > htp://tetlaw.id.au
> > _______________________________________________
> > Rails-spinoffs mailing list
> > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> >
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> >
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

-- 
Andrew Tetlaw
htp://tetlaw.id.au

Back to Sam''s original question, according to this:

http://www.stanford.edu/~newmanb/cs242_paper_deme.pdf

An object prototype cannot be changed after instantiation and there''s
not direct access for a programmer to an objects prototype.

This would explain why
MyObject.prototype.bSwitch = true
 works while
oObject1.prototype.bSwitch = true
doesn''t.

It also explains the error message: MyObject is indeed a function and
oObject is not. the only way to an objects prototype is via the
constructor function.


On 21/06/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
> // I thought all objects had prototypes.  Why doesn''t this work?
> oMyOb1.prototype.bSwitch = true;  // error:  oMyOb1 is not a function
>  Is there another method that I''ve missed?  Did prototype.js
extend
> __proto__ to work in IE?
>
> Sam
-- 
Andrew Tetlaw
htp://tetlaw.id.au

On 22/06/06, Sam <sam.google-Uc2IQQBAS6sAvxtiuMwx3w@public.gmane.org>
wrote:
> So... what does oMyInstance.contructor point to and how would I find out?
> ;-)
According to this page:

http://www.mozilla.org/docs/dom/mozilla/protodoc.html

oMyInstance.contructor points to the constructor function for the
object instance

But that Moz does not yet support using

oMyInstance.contructor.prototype.[property]



-- 
Andrew Tetlaw
htp://tetlaw.id.au

On 21/06/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> MyObject.prototype.bSwitch = true; is the correct way to achieve what you
> are looking for.
Personally I wouldn''t recommend doing this because of the potential
for confusion.

MyObject.prototype.bSwitch = true; is not exactly a class property
because each instance can be changed individually.

You can set it like this, sure
MyObject.prototype.bSwitch = true

and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch = true

But if you then set oMyInstance1.bSwitch = false; it''ll only change it
for the instance and not the class. Which means you are
reading/setting in different ways leading to potential
confusion/mistakes.

-- 
Andrew Tetlaw
htp://tetlaw.id.au

Right, but the original''s poster was looking for precisely a way to
chance a
property in the main function ("class") and have that change instantly
propagate to all instances.

On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> On 21/06/06, Ryan Gahl
<ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > MyObject.prototype.bSwitch = true; is the correct way to achieve what
> you
> > are looking for.
>
> Personally I wouldn''t recommend doing this because of the
potential
> for confusion.
>
> MyObject.prototype.bSwitch = true; is not exactly a class property
> because each instance can be changed individually.
>
> You can set it like this, sure
> MyObject.prototype.bSwitch = true
>
> and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch = true
>
> But if you then set oMyInstance1.bSwitch = false; it''ll only
change it
> for the instance and not the class. Which means you are
> reading/setting in different ways leading to potential
> confusion/mistakes.
>
> --
> Andrew Tetlaw
> htp://tetlaw.id.au
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>

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lol, no ides why i decided "original" should be a possisive
contraction.

On 6/22/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> Right, but the original''s poster was looking for precisely a way
to chance
> a property in the main function ("class") and have that change
instantly
> propagate to all instances.
>
> On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On 21/06/06, Ryan Gahl
<ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > MyObject.prototype.bSwitch = true; is the correct way to achieve
what
> > you
> > > are looking for.
> >
> > Personally I wouldn''t recommend doing this because of the
potential
> > for confusion.
> >
> > MyObject.prototype.bSwitch = true; is not exactly a class property
> > because each instance can be changed individually.
> >
> > You can set it like this, sure
> > MyObject.prototype.bSwitch = true
> >
> > and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch = true
> >
> > But if you then set oMyInstance1.bSwitch = false; it''ll only
change it
> > for the instance and not the class. Which means you are
> > reading/setting in different ways leading to potential
> > confusion/mistakes.
> >
> > --
> > Andrew Tetlaw
> > htp://tetlaw.id.au
> > _______________________________________________
> > Rails-spinoffs mailing list
> > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> >
>
>

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damnit... can''t type.. "possesive"

On 6/22/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> lol, no ides why i decided "original" should be a possisive
contraction.
>
>
> On 6/22/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> wrote:
> >
> > Right, but the original''s poster was looking for precisely a
way to
> > chance a property in the main function ("class") and have
that change
> > instantly propagate to all instances.
> >
> > On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> > > On 21/06/06, Ryan Gahl
<ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > > MyObject.prototype.bSwitch = true; is the correct way to
achieve
> > > what you
> > > > are looking for.
> > >
> > > Personally I wouldn''t recommend doing this because of
the potential
> > > for confusion.
> > >
> > > MyObject.prototype.bSwitch = true; is not exactly a class
property
> > > because each instance can be changed individually.
> > >
> > > You can set it like this, sure
> > > MyObject.prototype.bSwitch = true
> > >
> > > and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch =
true
> > >
> > > But if you then set oMyInstance1.bSwitch = false; it''ll
only change it
> > > for the instance and not the class. Which means you are
> > > reading/setting in different ways leading to potential
> > > confusion/mistakes.
> > >
> > > --
> > > Andrew Tetlaw
> > > htp://tetlaw.id.au
> > > _______________________________________________
> > > Rails-spinoffs mailing list
> > > Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> > > http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
> > >
> >
> >
>

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Which is what I think he''s saying as well.  You need to set it at a
class level, not at the object level.  Modifying the prototype will not
modify all of the instances (according to Andrew, haven''t verified it
or
anything, but I think he''s right).  So, if you set a class-level
Boolean
it should keep it''s state across all instances of that class.  Or maybe
I haven''t woken up yet :-)

 

Greg

 

________________________________

From: rails-spinoffs-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-spinoffs-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org]
On Behalf Of Ryan
Gahl
Sent: Thursday, June 22, 2006 7:27 AM
To: rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: Re: [Rails-spinoffs] Implementing a boolean "switch" in a
Class

 

Right, but the original''s poster was looking for precisely a way to
chance a property in the main function ("class") and have that change
instantly propagate to all instances.

On 6/21/06, Andrew Tetlaw
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

On 21/06/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> MyObject.prototype.bSwitch = true; is the correct way to achieve what
you
> are looking for.
Personally I wouldn''t recommend doing this because of the potential 
for confusion.

MyObject.prototype.bSwitch = true; is not exactly a class property
because each instance can be changed individually.

You can set it like this, sure
MyObject.prototype.bSwitch = true 

and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch = true

But if you then set oMyInstance1.bSwitch = false; it''ll only change it
for the instance and not the class. Which means you are
reading/setting in different ways leading to potential 
confusion/mistakes.

--
Andrew Tetlaw
htp://tetlaw.id.au
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Ok... I''m not sure why there''s a semi-debate going on here...

OP asked: "How can I set a value for a class such that all instances of
said
class get that value change automatically"

I said "you have to change a property on the main class''s
prototype... a la
MyClass.prototype.bSwitch = true;"

Yes, it gives rise to confusion later on and the OP will have to experience
this for himself... but if that''s what he wants, that''s how to
do it, and
that _is_ what he asked how to do.




On 6/22/06, Gregory Hill <Gregory_Hill-l9nu40+TWxQ@public.gmane.org>
wrote:
>
>  Which is what I think he''s saying as well.  You need to set it at
a class
> level, not at the object level.  Modifying the prototype will not modify
all
> of the instances (according to Andrew, haven''t verified it or
anything, but
> I think he''s right).  So, if you set a class-level Boolean it
should keep
> it''s state across all instances of that class.  Or maybe I
haven''t woken up
> yet J
>
>
>
> Greg
>
>
>   ------------------------------
>
> *From:*
rails-spinoffs-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:
> rails-spinoffs-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org]
*On Behalf Of *Ryan Gahl
> *Sent:* Thursday, June 22, 2006 7:27 AM
> *To:* rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> *Subject:* Re: [Rails-spinoffs] Implementing a boolean "switch"
in a Class
>
>
>
> Right, but the original''s poster was looking for precisely a way
to chance
> a property in the main function ("class") and have that change
instantly
> propagate to all instances.
>
> On 6/21/06, *Andrew Tetlaw*
<atetlaw-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> On 21/06/06, Ryan Gahl
<ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > MyObject.prototype.bSwitch = true; is the correct way to achieve what
> you
> > are looking for.
>
> Personally I wouldn''t recommend doing this because of the
potential
> for confusion.
>
> MyObject.prototype.bSwitch = true; is not exactly a class property
> because each instance can be changed individually.
>
> You can set it like this, sure
> MyObject.prototype.bSwitch = true
>
> and then oMyInstance1.bSwitch = true and oMyInstance2.bSwitch = true
>
> But if you then set oMyInstance1.bSwitch = false; it''ll only
change it
> for the instance and not the class. Which means you are
> reading/setting in different ways leading to potential
> confusion/mistakes.
>
> --
> Andrew Tetlaw
> htp://tetlaw.id.au
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>
> _______________________________________________
> Rails-spinoffs mailing list
> Rails-spinoffs-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails-spinoffs
>
>
>

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On 23/06/06, Gregory Hill <Gregory_Hill-l9nu40+TWxQ@public.gmane.org>
wrote:
> Modifying the prototype will not modify all
> of the instances (according to Andrew, haven''t verified it or
anything, but
> I think he''s right).
Actually, Ryan is right. I did a test and If you modify a prototype
object, existing instances of an object are updated. but you have to
do it via the constructor function object not an instance. Which I
think was confusing the original poster, Sam.

But you cannot change an objects prototype to another prototype.

here''s the test (using Firefox with firebug extension for the log):

function obj(name) {
	this.name = name;
}
obj.prototype.p = "x";
obj.prototype.x = function(){ return this.p };

var obj1 = new obj(''1'');
var obj2 = new obj(''2'');

console.log(obj1.name + ":" + obj1.x());
console.log(obj2.name + ":" + obj2.x());
console.log("switch...");

obj.prototype.p = "kk";
console.log(obj1.name + ":" + obj1.x());
console.log(obj2.name + ":" + obj2.x());

the output:

1:x
2:x
switch...
1:kk
2:kk




-- 
Andrew Tetlaw
htp://tetlaw.id.au

On 23/06/06, Ryan Gahl <ryan.gahl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Ok... I''m not sure why there''s a semi-debate going on
here...
>
Not a debate, just cooperative exploration.  :)


-- 
Andrew Tetlaw
htp://tetlaw.id.au