On 23.12.2010 11:49, Yu-Hsuan Lai wrote:
At my first sight, I were amazed at the prototypal concept in "Good
Part".
But when I tried to write little(very little) code, I'm confused.
Deeper I think about the skill, it looks more similar to classical...
My feeling is caused by a lack of understanding?
/Technically/, there is /no/ a big difference. Especially, if the
prototype chain doesn't change during the run-time, the resolution
difference is even less:
Prototypal: own -> proto -> proto -> proto -> null
Classical (abstractly): own -> class -> superclass -> superclass -> null.
The only big difference is /ideological/. In case of classical approach
the inheritance chain is linear (it's called a /tower/, a /vertical code
reuse/) and /systematized/ (or classified). In case of prototypal
inheritance -- the chain is not systematized (an object may inherit from
any object, which in turn inherits from another object -- at any step
this combination may rearrange and regroup in contrast with the
classical approach). There are no other very important differences (all
the other differences are cosmetic -- a needed sugar).
Notice, that in prototypal inheritance the inheritance chain is also
linear (as shown above). The ability to add a /horizontal code reuse/
(i.e. at every link of the inheritance chain, the link inherits
something /horizontally/) is provided by the /traits/ and /mixins/.
Thus, again, it may be done for both -- classical and prototypal systems.
own -> proto -> proto -> proto -> null
| | |
a c b
| |
b a
These a, b and c objects are /mixed/ to needed objects in the
inheritance chain. And again, at the end, one of the resolution
technique is make this chain as linear:
own -> proto -> a -> b -> proto -> c -> proto -> b -> a -> null
Absolutely the same can be done in classical approach (examples: Python,
Ruby).
I.e. the presence of the concept of a /class/ doesn't change much if
internally the /same techniques/ are used. A good example again is
Python -- it's a delegation based (the same as JS!) language, where
concept of a class is just a /syntactic sugar/. To see how this sugar is
implemented consider e.g. CoffeeScript which sugars the JS's
constructor+proto pair.
Are there some excellent open source project I should read to
understand javascript?
I can recommend my "Chapter 7. OOP." (there are two lectures "7.1. The
General Theory" where /all/ needed aspects are considered and "7.2.
ECMAScript implementation" devoted to exactly JS) of ES3 series. And (as
a brief but detailed lecture) "JavaScript. The Core."
Dmitry.
(Hmm... I know it's impossible to not open javascript's source code :)
On Thu, Dec 23, 2010 at 4:37 PM, Yu-Hsuan Lai <[email protected]
<mailto:[email protected]>> wrote:
In fact, even though I just want some public variants, I still
have the same problem.
var obj = {a:1,b:2,c:3 ... some methods...};
obj2 = Object.create(obj);
obj2.a is referred to obj.a, right? If I want another instance, I
have to write obj2.a = 1;
But if the object is very "big"? Write a function to assign all
variants? Is it "constructor"?
Once I implement these all, my prototypal OO still is different
from classical OO?
On Thu, Dec 23, 2010 at 3:14 PM, אריה גלזר <[email protected]
<mailto:[email protected]>> wrote:
This is exacatly the point - you create the methods and the
variable together, so either you get a copy of all of them, or
you get a new instance.
But if you want a 'private' variable for each instance, the
only way you are going to achieve this (I think) is by
creating a separate closure for each object creation. So you
can either do the above second solution, or you can do
var obj = {
getA : function getA() {
return this.a;
},
setA : function setA(b) {
a = this.b;
}
};
function F(){ this.a = 'a';}
for (i =0; i<10;i++) x.push((function(){ F.prototype = obj;
return new F();})();
And you will still be exposing a in the end. But the point is,
this is much less readable and performance-wise I don't think
it really matters, so your second pattern is good enough IMO.
note - this list beeing so heavy on js wizards, I'm always a
little afraid of posting comments here...
On Thu, Dec 23, 2010 at 8:23 AM, Yu-Hsuan Lai
<[email protected] <mailto:[email protected]>> wrote:
I'm trying use prototypal inheritance instead of classical
one. But I'm still confused.
I can't complete very very very small tasks, like this one:
Create 10 copies of a object(with a private variant and
public functions to access it) in an array.
I have two way to approach it, first is to use Object#create:
var x=[];
x[0]=(function () {
var a=10;
return {
getA : function getA() {
return a;
},
setA : function setA(b) {
a = b;
}
};
})();
for(var i=1; i<10; i++)
x[i] = Object.create(x[0]);
But all 10 objects' "a"s refer to a single integer. Tragedy.
My second way is call a function which return a object 10
times:
function createX() {
var a=10;
return {
getA : function getA() {
return a;
},
setA : function setA(b) {
a = b;
}
};
}
var x=[];
for(var i=0; i<10; i++)
x[i] = createX();
It works. But every x has its own "getA" and "setA"
instance. In contrast to the former, it costs more memory.
I know it maybe doesn't matter. But knowing prototypal OO
can use only one instance, creating 10 let me regard me as
a stupid.
Except the two methods, the only one method I can figure
out is... classical OO.
Is it avoidable?
--
Lai, Yu-Hsuan
--
To view archived discussions from the original JSMentors
Mailman list:
http://www.mail-archive.com/[email protected]/
To search via a non-Google archive, visit here:
http://www.mail-archive.com/[email protected]/
To unsubscribe from this group, send email to
[email protected]
<mailto:jsmentors%[email protected]>
--
Arieh Glazer
אריה גלזר
052-5348-561
http://www.arieh.co.il
http://www.link-wd.co.il
--
To view archived discussions from the original JSMentors
Mailman list: http://www.mail-archive.com/[email protected]/
To search via a non-Google archive, visit here:
http://www.mail-archive.com/[email protected]/
To unsubscribe from this group, send email to
[email protected]
<mailto:jsmentors%[email protected]>
--
Lai, Yu-Hsuan
--
Lai, Yu-Hsuan
--
To view archived discussions from the original JSMentors Mailman list:
http://www.mail-archive.com/[email protected]/
To search via a non-Google archive, visit here:
http://www.mail-archive.com/[email protected]/
To unsubscribe from this group, send email to
[email protected]
--
To view archived discussions from the original JSMentors Mailman list:
http://www.mail-archive.com/[email protected]/
To search via a non-Google archive, visit here:
http://www.mail-archive.com/[email protected]/
To unsubscribe from this group, send email to
[email protected]
