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Re: Reconciling handling of optional arguments and handling of default values across ES and webidl

From: Garrett Smith <dhtmlkitchen@gmail.com>
Date: Thu, 9 May 2013 12:09:10 -0700
Message-ID: <CABZUbM1HFW72x4VvY2PHZmm_OUHEuM2C57GUwi2fZ3hfVDoFHg@mail.gmail.com>
To: Boris Zbarsky <bzbarsky@mit.edu>
Cc: Andreas Rossberg <rossberg@google.com>, Allen Wirfs-Brock <allen@wirfs-brock.com>, "public-script-coord@w3.org" <public-script-coord@w3.org>
On 5/9/13, Boris Zbarsky <bzbarsky@mit.edu> wrote:
> On 5/9/13 11:11 AM, Andreas Rossberg wrote:
>> I think existing JS legacy notwithstanding it is generally bad
>> practice for an API to make an observable distinction between passing
>> undefined and not passing anything, especially in the light of ES6's
>> treatment of defaults. So I don't think a higher-level declarative
>> mechanism like WebIDL should ever want to support that.
>
> That was sort of my feeling too; just trying to figure out what the
> right spec language here is.
>
> Here's an interesting concrete example:
> CanvasRenderingContext2D.drawImage, which is specified like so at the
> moment:
Too much complexity from overloading and too many parameters. A value
object would be a consideration for API redesign.

>    drawImage(image, 0, 0, undefined);
>
> should do.  In today's world it throws.  Should WebIDL preserve the
> ability to do that in that situation?
>
According to the spec, it looks like that isn't valid but I don't see
what it says about what happens when four arguments are passed.
Likewise for two, six, seven, eight arguments. Normally, extra
arguments are ignored so anything over 9 might be predictable, but is
four arguments extra or not enough?

http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-drawimage
| This method can be invoked with three different sets of arguments:
|    drawImage(image, dx, dy)
|    drawImage(image, dx, dy, dw, dh)
|    drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh)
-- 
Garrett
Twitter: @xkit
personx.tumblr.com
Received on Thursday, 9 May 2013 19:09:37 UTC

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