----- Original Message -----
From: "Ian Hickson" <[EMAIL PROTECTED]>
To: "Andrew Fedoniouk" <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>; "Benjamin Joffe" <[EMAIL PROTECTED]>;
<[EMAIL PROTECTED]>
Sent: Sunday, July 02, 2006 12:59 PM
Subject: Re: [whatwg] Canvas 2d methods
On Sun, 2 Jul 2006, Andrew Fedoniouk wrote:
> On Sat, 1 Jul 2006, Andrew Fedoniouk wrote:
> >
> > In prototype based languages it is almost impossible to implement
> > 'with' effectively in the given notation.
> >
> > ctx.moveTo(0,0).lineTo(10,10);
> >
> > is more effective. In some circumstances - in times.
>
> Why is it more effective for JS?
foo.bar()
requires lookup only in foo and its proto chain. And
...for "bar". It still requires a complete lookup for "foo" in all the
parts of the scope chain.
1) if it is declared as
var foo = something; in current frame then
foo.bar();
foo.baz();
then execution is quite efficient.
But
with(something)
{
bar();
baz();
}
still requires scan of the whole universe in the worst case.
Consider this:
with(ctx)
{
bar( some_var_name );
}
runtime will scan full chain of ctx for some_var_name. What for?
--------------
something.bar().baz() is even more efficient than
var foo = something;
foo.bar();
foo.baz();
(Good bytecode optimizer can make it exactly something.bar().baz() but...)
with( foo ) { bar = 1; }
and foo does not contain that bar you need to scan whole namespace chain
(with case). In short 'with' creates additional level of ambiguity.
This is only the case where you don't know what "foo" will contain. In
this case what "foo" contains is very explicitly defined.
True. But evil is as always in worst cases.
Andrew Fedoniouk.
http://terrainformatica.com
