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WebIDL overload resolution, arrays and Nullable

From: Joshua Bell <jsbell@chromium.org>
Date: Fri, 29 Jun 2012 09:25:09 -0700
Message-ID: <CAD649j7UA7yrT-u=fHppVrEStccTaOO709seABcqspiHnVhEeg@mail.gmail.com>
To: public-webapps@w3.org
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?)
Received on Friday, 29 June 2012 16:25:37 GMT

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