[whatwg] Canvas 2d methods

[Andrew Fedoniouk]

----- Original Message ----- 
From: "Ian Hickson" <ian at hixie.ch>
To: "Andrew Fedoniouk" <news at terrainformatica.com>
Cc: <vladimir at pobox.com>; "Benjamin Joffe" <canvasgame at gmail.com>; 
<whatwg at whatwg.org>
Sent: Saturday, July 01, 2006 10:21 PM
Subject: Re: [whatwg] Canvas 2d methods


> 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

with(foo) {  bar() }

requires lookup in 'with stack', current function namespace
and stack of global namespaces.

When foo contains bar and you are doing lookup for read these cases
are almost identical but if you have something like

foo.bar = 1;

and

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.

In case of ctx.moveTo(0,0).lineTo(10,10);  bytecode structure looks close
to this:

BC_GET 'ctx' <- put ctx  on top of the stack.
BC_CALL_METHOD 'moveTo' <- call method 'moveTo'  of the
                   object on top of the stack.  Put result on top of the 
stack.
BC_CALL_METHOD 'lineTo' <- call method 'lineTo' of the
                   object on top of the stack.....

And yet 'with' accepts list of arguments...

Andrew Fedoniouk.
http://terrainformatica.com