thx for the great explanation!
On Sat, Feb 23, 2008 at 11:07 AM, T.J. Crowder <[EMAIL PROTECTED]> wrote:
>
> Oops, this:
>
> > Since the closure holds a
> > reference to all of myNiftyMethods local variables and params (even
> > though it doesn't use them), and since the object instance keeps a
> > reference to the closure, 'param', 'v1', 'v2', and 'v3' all live on
> > for as long as the closure does.
>
> ...should end with "as long as the object instance does, or until
> this.thingy is cleared."
>
> (Proofread, *then* post.)
>
> -- T.J. ;-)
>
> On Feb 23, 10:01 am, "T.J. Crowder" <[EMAIL PROTECTED]> wrote:
> > Hi,
> >
> > > Closures is something that (can) cause memory leaks, right?
> >
> > That's a complex topic. :-) Closures inherit, and therefore preserve
> > for their lifecycles, all of the local variables and parameters of the
> > functions they're defined in. If the closure is used immediately and
> > discarded, you don't much care. If you're going to retain a reference
> > to the closure (for instance, an event handler, or a dynamically-
> > created instance method), then you want to be aware of this. Here's
> > an example of the latter case:
> >
> > function myNiftyMethod(param)
> > {
> > var v1, v2, v3;
> >
> > // ... do something ...
> >
> > // create and retain a closure to do something
> > this.thingy = function() {
> > // ... some code for the closure ...
> > };
> >
> > }
> >
> > When myNiftyMethod is executed, it creates a closure and remembers it
> > on the object instance as this.thingy. Since the closure holds a
> > reference to all of myNiftyMethods local variables and params (even
> > though it doesn't use them), and since the object instance keeps a
> > reference to the closure, 'param', 'v1', 'v2', and 'v3' all live on
> > for as long as the closure does. (Modulo cool JavaScript engine
> > optimisations, which I don't think are common yet and are harder for
> > the engine to do than it would at first seem.)
> >
> > So closures can have memory *implications*; if you understand how they
> > work, though, and get used to some idioms around them, you won't cause
> > memory leaks (barring JavaScript engine bugs).
> >
> > This is rambling a bit, but here's an example of the case where you're
> > using the closure immediately and discarding it:
> >
> > function myNiftyMethod(someArray)
> > {
> > var v1, v2, v3;
> >
> > // ... do something ...
> >
> > // create and retain a closure to do something
> > someArray.each(function(item) {
> > item.doSomethingCool();
> > });
> >
> > }
> >
> > You don't keep a reference to the closure used in the each() method,
> > so you don't have to consider the implications of myNiftyMethod's
> > parameters and variables being retained. And it's a very powerful and
> > expressive way to deal with each item in the array.
> >
> > > - I'm getting lost in how you constructed the onSuccess callback...
> >
> > That's easy to do. :-) He's using a closure to construct and return
> > another closure; it's the inner one that gets assigned to the
> > onSuccess handler and retained, the outer one is run immediately and
> > discarded. If you look carefully at the code defining the onSuccess
> > handler, you'll see that the entire outer closure is wrapped in parens
> > -- the opening paren is right after "onSuccess:", and then right at
> > the end of the closure you see the closing paren followed by "(item)"
> > -- that "(item)" tells you he's *executing* the outer closure right
> > then, not just creating it. When it runs, the outer closure creates
> > the inner closure and returns it. *That's* what gets assigned to
> > onSuccess, the reference to the inner closure. The outer closure has
> > only the param it needs (item) and no local variables, so the inner
> > closure only preserves the information it really needs, not all of the
> > local variables where all of this is running.
> >
> > Hope this helps,
> > --
> > T.J. Crowder
> > tj /crowder software / com
> >
> > On Feb 23, 7:34 am, "Manu Temmerman-Uyttenbroeck"
> >
> > <[EMAIL PROTECTED]> wrote:
> > > Hi,
> >
> > > Closures is something that (can) cause memory leaks, right?
> > > kangax, would you mind explaining in a bit more detail why you wrote
> the
> > > code like you wrote it? I'm a bit lost in it. I restructured the code
> you
> > > wrote a bit...http://pastie.caboo.se/156248
> > > - Is there a reason why you don't write a ';' after the new
> Ajax.Request
> > > (...)?
> > > - Is there a reason why you don't write a ';' after the
> > > someArray.each(function(item)
> > > { ... })?
> > > - I'm getting lost in how you constructed the onSuccess callback...
> >
> > > Thx...
> >
> > > Manu.
> >
> > > On Fri, Feb 22, 2008 at 11:11 PM, kangax <[EMAIL PROTECTED]> wrote:
> >
> > > > Looks like a closure issue to me (solved with another closure).
> > > > Also, is that an array you are iterating over using "for..in" ?
> >
> > > > siteListArray.each(function(item) {
> > > > var url = 'functions.php?command=numberOfErrors&site=' + item;
> > > > new Ajax.Request(url, {
> > > > onSuccess: (function(item) { return function(t) {
> > > > $('sidebar_site_div_' + item).update(t.responseText);
> > > > }})(item)
> > > > })
> > > > })
> >
> > > > - kangax
> >
> > > > On Feb 22, 4:02 pm, Chach <[EMAIL PROTECTED]> wrote:
> > > > > Hi everybody,
> >
> > > > > I'm just getting kicked off on prototype and I'm having a problem
> that
> > > > > I'm hoping to get some help on.. I've had good success with
> > > > > Ajax.Updater, but now I'm trying to use Ajax.Request with the use
> of
> > > > > its callback abilities. My issue is that I'm trying to get a hold
> of
> > > > > one of the Element objects in the DOM using $('element'), however
> the
> > > > > name of the element can vary and so I have to assemble the name
> using
> > > > > the value in an array. It's almost like the siteListArray[x] does
> not
> > > > > work in the callback. Is it possible that the callback cannot see
> a
> > > > > variable that was declared earlier in my code at a global scope?
> > > > > Thanks in advance.
> >
> > > > > for (x in siteListArray)
> > > > > {
> > > > > var url = 'functions.php?command=numberOfErrors&site=' +
> > > > > siteListArray[x];
> > > > > new Ajax.Request(url, {
> > > > > asynchronous:true,
> > > > > onComplete: function(transport) {
> > > > > $('sidebar_site_div_' +
> > > > > siteListArray[x]).update(transport.responseText);
> > > > > }
> > > > > });
> >
> > > > > }
> >
>
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "Ruby
on Rails: Spinoffs" 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/rubyonrails-spinoffs?hl=en
-~----------~----~----~----~------~----~------~--~---
