> I need to acces to private variables in my class like in C#
> How can I realize it in Prototype?
Prototype doesn't give you anything here, so you're just looking at
how to do it with JavaScript.
JavaScript doesn't have private variables. The equivalent of private
*class* variables (e.g., statics in C#) is very easy to emulate using
the module pattern. Private *instance* variables, as in your C#
example code, you can emulate using closures[1], but at the expense
that any function that needs access to the private variable will be
*duplicated* for every instance of your object.
Example:
var Thingy = Class.create({
initialize: function() {
var trulyPrivate = 0;
this.getNextPrivateValue = function() {
return ++trulyPrivate;
};
},
doSomething: function() {
// This does *not* have access to `trulyPrivate`
}
});
(http://jsbin.com/oleko6/2)
Every instance of the `Thingy` "class" has a truly private variable,
the `trulyPrivate` local variable within `initialize`. `Thingy` has
only one function that can access it, the `getNextPrivateValue`
function. (Well, okay, two; `initialize` can access it as well, of
course!) The `getNextPrivateValue` function is created within
`initialize` and so it closes over that local variable, which can't be
seen from outside. Because the closure endures after the return from
`initialize`, so does the variable, because it exists on something
called the "variable object" for the call to `initialize`, which the
closure has an enduring reference to. That means it can read and write
that variable, even though it's not a property of the instance.
Note that `doSomething` doesn't have access to `trulyPrivate`, because
the only things it has access to within the instance would be through
its `this` reference, which has only the properties that anything else
(outside `Thingy`) can see. This is a consequence of the fact that
JavaScript doesn't have methods, it just has functions.[2]
The cost is that the `getNextPrivateValue` function is created for
*every* instance of `Thingy`. So if you create 20 `Thingy` instances,
you'll have 20 copies of the `getNextPrivateValue` function in memory.
That's fine if you're only going to have a few of these things in
memory at any given time; if you're going to have hundreds or
thousands of them, that's probably not fine and you should just use a
property that you tell people not to touch.
[1] http://blog.niftysnippets.org/2008/02/closures-are-not-complicated.html
[2] http://blog.niftysnippets.org/2008/03/mythical-methods.html
HTH,
--
T.J. Crowder
Independent Software Engineer
tj / crowder software / com
www / crowder software / com
On Mar 7, 7:05 am, buda <[email protected]> wrote:
> I need to acces to private variables in my class like in C#
>
> ...
> protected bool _visible;
> public bool Visible
> {
> get
> {
> return _visible;
> }
> set
> {
> _visible = value;
> }
> }
>
> How can I realize it in Prototype?
> Thanks!
--
You received this message because you are subscribed to the Google Groups
"Prototype & script.aculo.us" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/prototype-scriptaculous?hl=en.
