W3C home > Mailing lists > Public > public-webapps@w3.org > April to June 2012

Re: WebIDL overload resolution, arrays and Nullable

From: Kyle Huey <me@kylehuey.com>
Date: Fri, 29 Jun 2012 09:37:13 -0700
Message-ID: <CAP045Ap3-2vkVaY=H4xqSk7ptUnGGnmde-7KS1qzTcaLWz=ycg@mail.gmail.com>
To: Joshua Bell <jsbell@chromium.org>
Cc: public-webapps@w3.org
On Fri, Jun 29, 2012 at 9:25 AM, Joshua Bell <jsbell@chromium.org> wrote:

> Over in WebKit-land there's some disagreement about WebIDL method overload
> resolution, specifically around passing null, arrays (T[]) and the concept
> of Nullable.
> Here's an example where we're just not sure what the WebIDL spec dictates:
> void f(float[] x); // overload A
> void f(DOMString x); // overload B
> WebIDL itself, of course, doesn't dictate how matching and dispatching
> should be implemented; it instead defines whether types are
> distinguishable. The implication is that an IDL that defines methods with
> signatures that are not distinguishable is invalid, so it's a non-issue in
> terms of the spec. So rephrasing the question: are the above types
> distinguishable? And if so, which would be expected to handle the call:
> f(null);
> Several interpretations and hence outcomes occur to us, hopefully
> presented without indicating my particular bias:
> (1) T[] is inherently Nullable (i.e. T[] === T[]?), DOMString is not,
> overload A would be invoked with a null argument and the implementation is
> expected to handle this case
> (2) T[] accepts null but the IDL type to ECMAScript conversion rules
> produce an empty array; overload A is invoked with an empty float array
> (3) T[] does not match null, but as null is an ECMAScript primitive value
> it is run through ToString() and hence overload B is invoked with DOMString
> "null"
> (4) Either T[] or DOMString could match null, so types of the arguments
> are not distinguishable and hence the above is invalid WebIDL
> (5) Neither T[] nor DOMString is inherently Nullable, so a TypeError is
> thrown
> Anyone? (Cameron?)

#5.  Neither T[] nor DOMString admits null as a value.

"Note also that null is not a value of type DOMString. To allow null, a
nullable DOMString, written as DOMString? in IDL, needs to be used. "


"The T[] type is a parameterized type. The values of this type are non-null
references to arrays of values of type T."


- Kyle
Received on Friday, 29 June 2012 16:37:42 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 18:13:34 UTC