[webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
This is a followup to the multiple inheritance discussion.
Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not have
multiple inheritances of interfaces that are exposed to bindings. But SVG2
still uses the implements statement for [NoInterfaceObject] interfaces [2].
This should at least address your initial concern not to inherit from different
interfaces exposed to bindings.
However, during a discussion on IRC I got the impression that we do not plan to
support the implements statement because it can do weird things. If this is
right, I would like to understand why this is the case? Have the concerns been
submitted to the editor and the WG working on the WebIDL specification?
More and more specifications describe interfaces by using WebIDL, including
HTML5, Canvas, SVG2, Filter Effects and CSS Masking. If there are general
concerns on WebIDL, they should be addressed on the spec before leaving CR
state. Not implementing WebIDL could not only block this specification in
particular, but also all other specs relying on it. Or maybe worst, it gets a
recommendation and we do not follow web standards anymore. It would be great to
hear a clarification. Maybe it is just a misunderstanding on my site.
Greetings,
Dirk
[1]
https://svgwg.org/svg2-draft/single-page.html#types-InterfaceSVGGraphicsElement
[2] http://www.w3.org/TR/WebIDL/#NoInterfaceObject
On Jul 25, 2012, at 9:13 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jul 25, 2012, at 3:50 PM, Adam Barth wrote:
On Wed, Jul 25, 2012 at 3:44 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jul 25, 2012, at 2:33 PM, Adam Barth wrote:
Eric Seidel points out that SVG uses multiple inheritance in its DOM
interfaces. However, the situation there is a bit different.
Although SVGSVGElement implements SVGLocatable, there aren't any
interfaces with methods that return SVGLocatable, which means we don't
need to implement toJS(SVGLocatable*).
SVG 2 will use WebIDL. Therefore we also reorganize our inheritance
behavior. Cameron, editor of WebIDL and SVG WG member, will update SVG 2 ED
soon.
Do you anticipate adding properties or functions that return
interfaces like SVGLocatable?
Here is a Wiki what we plan to do:
http://www.w3.org/Graphics/SVG/WG/wiki/Proposals/IDL_interface_reorganization
It might not reflect all changes that we discussed during the SVG WG meeting
today.
Greetings,
Dirk
Adam
He also points out that Node inherits from EventTarget, which already
contains a virtual interfaceName() function similar to that used by
Event. That pushes us further towards using a common DOMInterface
base class because introducing Region::interfaceName would mean that
Element would see both EventTarget::interfaceName and
Region::interfaceName.
Adam
On Wed, Jul 25, 2012 at 2:00 PM, Adam Barth aba...@webkit.org wrote:
The CSS Regions specification [1] defines a CSSOM interface named
Region, which can be mixed into interfaces for other objets that can
be CSS regions. That means that Region introduces a form of multiple
inheritance into the DOM. For example, Element implements Region but
Node does not implement Region.
There's a patch up for review that implements Region using C++
multiple inheritance [2]:
- class Element : public ContainerNode {
+ class Element : public ContainerNode, public CSSRegion {
One difficulty in implementing this feature how to determine the
correct JavaScript wrapper return for a given Region object.
Specifically, toJS(Region*) needs to return a JavaScript wrapper for
an Element if the Region pointer actually points to an Element
instance.
We've faced a similar problem elsewhere in the DOM when implementing
normal single inheritance. For example, there are many subclass of
Event and toJS(Event*) needs to return a wrapper for the appropriate
subtype. To solve the same problem, CSSRule has a m_type member
variable and a bevy of isFoo() functions [3].
A) Should we push back on the folks writing the CSS Regions
specification to avoid using multiple inheritance? As far as I know,
this is the only instance of multiple inheritance in the platform.
Historically, EventTarget used multiple inheritance, but that's been
fixed in DOM4 [4].
B) If CSS Regions continues to require multiple inheritance, should we
build another one-off RTTI replacement to implement toJS(Region*), or
should we improve our bindings to implement this aspect of WebIDL more
completely?
One approach to implementing toJS in a systematic way is to introduce
a base class DOMInterface along these lines:
class DOMInterface {
public:
virtual const AtomicString primaryInterfaceName() = 0;
}
That returns the name of the primary interface (i.e., as defined by
WebIDL [5]). When implementing toJS, we'd then call
primaryInterfaceName to determine which kind of wrapper to use.
One downside of this approach is that it introduces a near-universal
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com wrote:
This is a followup to the multiple inheritance discussion.
Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not
have multiple inheritances of interfaces that are exposed to bindings. But
SVG2 still uses the implements statement for [NoInterfaceObject]
interfaces [2]. This should at least address your initial concern not to
inherit from different interfaces exposed to bindings.
However, during a discussion on IRC I got the impression that we do not plan
to support the implements statement because it can do weird things. If
this is right, I would like to understand why this is the case?
We don't intend to support all the possible things that you can do
with implements. With implements, you can define arbitrarily
complicated relationships between interfaces, including some that can
be implemented only with a QueryInterface-like mechanism. We're not
going to implement QueryInterface, so we're not going to implement any
specifications that require it.
Have the concerns been submitted to the editor and the WG working on the
WebIDL specification?
I haven't submitted my concerns. There's nothing particularly wrong
with the WebIDL language, just like there's nothing particularly wrong
with English just because you can use it to write a terrible poem.
More and more specifications describe interfaces by using WebIDL, including
HTML5, Canvas, SVG2, Filter Effects and CSS Masking. If there are general
concerns on WebIDL, they should be addressed on the spec before leaving CR
state.
I don't have any concerns with the WebIDL language. The WebIDL
language is just a mechanism for writing precise specifications.
Not implementing WebIDL could not only block this specification in
particular, but also all other specs relying on it.
That's nonsense. Just because we don't implement some crazy corner
case of WebIDL that doesn't mean that we're unable to implement *all*
specs that reply upon it. For example, HTML and DOM use WebIDL and
we're able to implement them just fine.
Or maybe worst, it gets a recommendation and we do not follow web standards
anymore. It would be great to hear a clarification. Maybe it is just a
misunderstanding on my site.
There's no experiment that you can run using web content to detect
whether we implement WebIDL. All you can detect is whether we
implement particular specifications that use WebIDL. We can just
simply not implement the specifications that require COM-like
implementations and we can continue to lead a happy life.
Adam
On Jul 25, 2012, at 9:13 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jul 25, 2012, at 3:50 PM, Adam Barth wrote:
On Wed, Jul 25, 2012 at 3:44 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jul 25, 2012, at 2:33 PM, Adam Barth wrote:
Eric Seidel points out that SVG uses multiple inheritance in its DOM
interfaces. However, the situation there is a bit different.
Although SVGSVGElement implements SVGLocatable, there aren't any
interfaces with methods that return SVGLocatable, which means we don't
need to implement toJS(SVGLocatable*).
SVG 2 will use WebIDL. Therefore we also reorganize our inheritance
behavior. Cameron, editor of WebIDL and SVG WG member, will update SVG 2
ED soon.
Do you anticipate adding properties or functions that return
interfaces like SVGLocatable?
Here is a Wiki what we plan to do:
http://www.w3.org/Graphics/SVG/WG/wiki/Proposals/IDL_interface_reorganization
It might not reflect all changes that we discussed during the SVG WG meeting
today.
Greetings,
Dirk
Adam
He also points out that Node inherits from EventTarget, which already
contains a virtual interfaceName() function similar to that used by
Event. That pushes us further towards using a common DOMInterface
base class because introducing Region::interfaceName would mean that
Element would see both EventTarget::interfaceName and
Region::interfaceName.
Adam
On Wed, Jul 25, 2012 at 2:00 PM, Adam Barth aba...@webkit.org wrote:
The CSS Regions specification [1] defines a CSSOM interface named
Region, which can be mixed into interfaces for other objets that can
be CSS regions. That means that Region introduces a form of multiple
inheritance into the DOM. For example, Element implements Region but
Node does not implement Region.
There's a patch up for review that implements Region using C++
multiple inheritance [2]:
- class Element : public ContainerNode {
+ class Element : public ContainerNode, public CSSRegion {
One difficulty in implementing this feature how to determine the
correct JavaScript wrapper return for a given Region object.
Specifically, toJS(Region*) needs to return a JavaScript wrapper for
an Element if the Region pointer actually points to an Element
instance.
We've faced a similar problem elsewhere in the DOM when implementing
normal single inheritance. For example, there are
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 10:14 AM, Adam Barth aba...@webkit.org wrote:
There's no experiment that you can run using web content to detect
whether we implement WebIDL. All you can detect is whether we
implement particular specifications that use WebIDL. We can just
simply not implement the specifications that require COM-like
implementations and we can continue to lead a happy life.
Speaking of implementing WebIDL (in the context of a spec that normatively
requires its support, e.g., CSSOM), what is your position on whether WK
will/should support the following? In the test at [1], neither of these are
currently supported, or at least don't yield expected results.
WebIDL 4.4.1 [2] states:
The interface object for a given non-callback
interfacehttp://dev.w3.org/2006/webapi/WebIDL/#dfn-interface is
a function objecthttp://dev.w3.org/2006/webapi/WebIDL/#dfn-function-object
.
WebIDL 4.4.3 [3] states:
If the
[NoInterfaceObject]http://dev.w3.org/2006/webapi/WebIDL/#NoInterfaceObject
extended
attribute was not specified on the interface, then the interface prototype
object must also have a property named “constructor” with attributes
{ [[Writable]]:true, [[Enumerable]]: false, [[Configurable]]: true } whose
value is a reference to the interface object for the interface.
[1]
http://hg.csswg.org/test/raw-file/3d8f9c12b1c8/contributors/gadams/incoming/cssom/cssstylerule-interface.xht
[2] http://dev.w3.org/2006/webapi/WebIDL/#interface-object
[3] http://dev.w3.org/2006/webapi/WebIDL/#interface-prototype-object
Regards,
Glenn
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Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Jan 25, 2013, at 9:14 AM, Adam Barth aba...@webkit.org wrote: On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com wrote: This is a followup to the multiple inheritance discussion. Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not have multiple inheritances of interfaces that are exposed to bindings. But SVG2 still uses the implements statement for [NoInterfaceObject] interfaces [2]. This should at least address your initial concern not to inherit from different interfaces exposed to bindings. However, during a discussion on IRC I got the impression that we do not plan to support the implements statement because it can do weird things. If this is right, I would like to understand why this is the case? We don't intend to support all the possible things that you can do with implements. With implements, you can define arbitrarily complicated relationships between interfaces, including some that can be implemented only with a QueryInterface-like mechanism. We're not going to implement QueryInterface, so we're not going to implement any specifications that require it. This sounds that you consider having implements in our WebIDL interpreter, or at least would not block adding this per se. This was my concern in the first place, since this is already in use in a lot of specifications (just with [NoInterfaceObject] as far as I saw). Have the concerns been submitted to the editor and the WG working on the WebIDL specification? I haven't submitted my concerns. There's nothing particularly wrong with the WebIDL language, just like there's nothing particularly wrong with English just because you can use it to write a terrible poem. Well, it seems to be a bit different. Your poem would still be valid as long as it follows the grammar and can still be read, even if it does not make sense to you. You suggest not supporting everything from WebIDL, which means not accepting the full specified grammar. I think this is a concern where you would like to see limitations to the current grammar and which should be discussed. More and more specifications describe interfaces by using WebIDL, including HTML5, Canvas, SVG2, Filter Effects and CSS Masking. If there are general concerns on WebIDL, they should be addressed on the spec before leaving CR state. I don't have any concerns with the WebIDL language. The WebIDL language is just a mechanism for writing precise specifications. Not implementing WebIDL could not only block this specification in particular, but also all other specs relying on it. That's nonsense. Just because we don't implement some crazy corner case of WebIDL that doesn't mean that we're unable to implement *all* specs that reply upon it. For example, HTML and DOM use WebIDL and we're able to implement them just fine. You suggest not implementing some corner cases. And as you say, we won't be able to support specifications relying on these corner cases. It rather seems you agree with my statement, even if it does not block former named specifications yet. I am not questioning your arguments to not support all corner cases of WebIDL. I am asking for an open discussion about particular cases on the relevant mailing lists (public-webapps for WebIDL) to address these concerns in the specification before leaving CR. Or maybe worst, it gets a recommendation and we do not follow web standards anymore. It would be great to hear a clarification. Maybe it is just a misunderstanding on my site. There's no experiment that you can run using web content to detect whether we implement WebIDL. All you can detect is whether we implement particular specifications that use WebIDL. We can just simply not implement the specifications that require COM-like implementations and we can continue to lead a happy life. This seems indeed a problem for WebIDL, since tests and testability is a requirement to leave CR. However, the WebApps WG might have a different thought. Greetings, Dirk Adam On Jul 25, 2012, at 9:13 PM, Dirk Schulze dschu...@adobe.com wrote: On Jul 25, 2012, at 3:50 PM, Adam Barth wrote: On Wed, Jul 25, 2012 at 3:44 PM, Dirk Schulze dschu...@adobe.com wrote: On Jul 25, 2012, at 2:33 PM, Adam Barth wrote: Eric Seidel points out that SVG uses multiple inheritance in its DOM interfaces. However, the situation there is a bit different. Although SVGSVGElement implements SVGLocatable, there aren't any interfaces with methods that return SVGLocatable, which means we don't need to implement toJS(SVGLocatable*). SVG 2 will use WebIDL. Therefore we also reorganize our inheritance behavior. Cameron, editor of WebIDL and SVG WG member, will update SVG 2 ED soon. Do you anticipate adding properties or functions that return interfaces like SVGLocatable? Here is a Wiki what we plan to do:
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 11:28 AM, Glenn Adams gl...@skynav.com wrote:
On Fri, Jan 25, 2013 at 10:14 AM, Adam Barth aba...@webkit.org wrote:
There's no experiment that you can run using web content to detect
whether we implement WebIDL. All you can detect is whether we
implement particular specifications that use WebIDL. We can just
simply not implement the specifications that require COM-like
implementations and we can continue to lead a happy life.
Speaking of implementing WebIDL (in the context of a spec that normatively
requires its support, e.g., CSSOM), what is your position on whether WK
will/should support the following? In the test at [1], neither of these are
currently supported, or at least don't yield expected results.
WebIDL 4.4.1 [2] states:
The interface object for a given non-callback interface is a function
object.
WebIDL 4.4.3 [3] states:
If the [NoInterfaceObject] extended attribute was not specified on the
interface, then the interface prototype object must also have a property
named “constructor” with attributes { [[Writable]]:true, [[Enumerable]]:
false, [[Configurable]]: true } whose value is a reference to the interface
object for the interface.
I don't have a strong opinion on those topics. I'm happy to review
patches in this area.
Adam
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Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 2:08 PM, Dirk Schulze dschu...@adobe.com wrote: On Jan 25, 2013, at 9:14 AM, Adam Barth aba...@webkit.org wrote: On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com wrote: This is a followup to the multiple inheritance discussion. Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not have multiple inheritances of interfaces that are exposed to bindings. But SVG2 still uses the implements statement for [NoInterfaceObject] interfaces [2]. This should at least address your initial concern not to inherit from different interfaces exposed to bindings. However, during a discussion on IRC I got the impression that we do not plan to support the implements statement because it can do weird things. If this is right, I would like to understand why this is the case? We don't intend to support all the possible things that you can do with implements. With implements, you can define arbitrarily complicated relationships between interfaces, including some that can be implemented only with a QueryInterface-like mechanism. We're not going to implement QueryInterface, so we're not going to implement any specifications that require it. This sounds that you consider having implements in our WebIDL interpreter, or at least would not block adding this per se. This was my concern in the first place, since this is already in use in a lot of specifications (just with [NoInterfaceObject] as far as I saw). WebKit doesn't have an WebIDL interpretor. We have a WebKitIDL compiler. If you spec something that requires a QueryInterface-like mechanism in the implementation, we will not implement it regardless of what language you write the specification in. It's a conscious design decision not to implement a COM-like (or XPCOM-like) system. Have the concerns been submitted to the editor and the WG working on the WebIDL specification? I haven't submitted my concerns. There's nothing particularly wrong with the WebIDL language, just like there's nothing particularly wrong with English just because you can use it to write a terrible poem. Well, it seems to be a bit different. Your poem would still be valid as long as it follows the grammar and can still be read, even if it does not make sense to you. You suggest not supporting everything from WebIDL, which means not accepting the full specified grammar. I think this is a concern where you would like to see limitations to the current grammar and which should be discussed. In this analogy, WebKit is like a collection of poems. We can choose not to include a terrible poem in our collection without needing to form a judgement about the language in which the poem was written. More and more specifications describe interfaces by using WebIDL, including HTML5, Canvas, SVG2, Filter Effects and CSS Masking. If there are general concerns on WebIDL, they should be addressed on the spec before leaving CR state. I don't have any concerns with the WebIDL language. The WebIDL language is just a mechanism for writing precise specifications. Not implementing WebIDL could not only block this specification in particular, but also all other specs relying on it. That's nonsense. Just because we don't implement some crazy corner case of WebIDL that doesn't mean that we're unable to implement *all* specs that reply upon it. For example, HTML and DOM use WebIDL and we're able to implement them just fine. You suggest not implementing some corner cases. And as you say, we won't be able to support specifications relying on these corner cases. It rather seems you agree with my statement, even if it does not block former named specifications yet. You're welcome to write whatever specifications you like. I'm just hoping to save you the effort by telling you that we're not going to implement a feature that requires us to build COM. I am not questioning your arguments to not support all corner cases of WebIDL. I am asking for an open discussion about particular cases on the relevant mailing lists (public-webapps for WebIDL) to address these concerns in the specification before leaving CR. I have no concerns with WebIDL. I have concerns with specifications that require an implementation of QueryInterface regardless of whether they're written in WebIDL or in English. Adam On Jul 25, 2012, at 9:13 PM, Dirk Schulze dschu...@adobe.com wrote: On Jul 25, 2012, at 3:50 PM, Adam Barth wrote: On Wed, Jul 25, 2012 at 3:44 PM, Dirk Schulze dschu...@adobe.com wrote: On Jul 25, 2012, at 2:33 PM, Adam Barth wrote: Eric Seidel points out that SVG uses multiple inheritance in its DOM interfaces. However, the situation there is a bit different. Although SVGSVGElement implements SVGLocatable, there aren't any interfaces with methods that return SVGLocatable, which means we don't need to implement toJS(SVGLocatable*). SVG 2 will use WebIDL. Therefore we also reorganize
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Jan 25, 2013, at 4:13 PM, Adam Barth aba...@webkit.org wrote: On Fri, Jan 25, 2013 at 2:08 PM, Dirk Schulze dschu...@adobe.com wrote: On Jan 25, 2013, at 9:14 AM, Adam Barth aba...@webkit.org wrote: On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com wrote: This is a followup to the multiple inheritance discussion. Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not have multiple inheritances of interfaces that are exposed to bindings. But SVG2 still uses the implements statement for [NoInterfaceObject] interfaces [2]. This should at least address your initial concern not to inherit from different interfaces exposed to bindings. However, during a discussion on IRC I got the impression that we do not plan to support the implements statement because it can do weird things. If this is right, I would like to understand why this is the case? We don't intend to support all the possible things that you can do with implements. With implements, you can define arbitrarily complicated relationships between interfaces, including some that can be implemented only with a QueryInterface-like mechanism. We're not going to implement QueryInterface, so we're not going to implement any specifications that require it. This sounds that you consider having implements in our WebIDL interpreter, or at least would not block adding this per se. This was my concern in the first place, since this is already in use in a lot of specifications (just with [NoInterfaceObject] as far as I saw). WebKit doesn't have an WebIDL interpretor. We have a WebKitIDL compiler. If you spec something that requires a QueryInterface-like mechanism in the implementation, we will not implement it regardless of what language you write the specification in. It's a conscious design decision not to implement a COM-like (or XPCOM-like) system. Setting aside the more general question, does the SVG2 set of interfaces effectively require a QueryInterface-like mechanism? What limitations, if any, on the use of implements would a spec have to follow to dodge this bullet? SVG2 is still evolving, so I suspect it could adjust its use of implements if it's an issue for us. If SVG2 does happen to avoid the problem, would we want to use implements as the syntax in WebKitIDL or would we want a different syntax? I could see arguments either way. (FWIW I agree that we don't want to end up in a position where we'd have to implement a QI-like mechanism for the sake of the bindings, but I can't tell from the conversation so far if this is an immediate issue with SVG2, or just a possible issue with other potential uses of implements). Regards, Maciej ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Jan 25, 2013, at 4:23 PM, Maciej Stachowiak m...@apple.com wrote:
On Jan 25, 2013, at 4:13 PM, Adam Barth aba...@webkit.org wrote:
On Fri, Jan 25, 2013 at 2:08 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jan 25, 2013, at 9:14 AM, Adam Barth aba...@webkit.org wrote:
On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com wrote:
This is a followup to the multiple inheritance discussion.
Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2 do not
have multiple inheritances of interfaces that are exposed to bindings.
But SVG2 still uses the implements statement for [NoInterfaceObject]
interfaces [2]. This should at least address your initial concern not to
inherit from different interfaces exposed to bindings.
However, during a discussion on IRC I got the impression that we do not
plan to support the implements statement because it can do weird
things. If this is right, I would like to understand why this is the case?
We don't intend to support all the possible things that you can do
with implements. With implements, you can define arbitrarily
complicated relationships between interfaces, including some that can
be implemented only with a QueryInterface-like mechanism. We're not
going to implement QueryInterface, so we're not going to implement any
specifications that require it.
This sounds that you consider having implements in our WebIDL
interpreter, or at least would not block adding this per se. This was my
concern in the first place, since this is already in use in a lot of
specifications (just with [NoInterfaceObject] as far as I saw).
WebKit doesn't have an WebIDL interpretor. We have a WebKitIDL
compiler. If you spec something that requires a QueryInterface-like
mechanism in the implementation, we will not implement it regardless
of what language you write the specification in. It's a conscious
design decision not to implement a COM-like (or XPCOM-like) system.
Setting aside the more general question, does the SVG2 set of interfaces
effectively require a QueryInterface-like mechanism? What limitations, if
any, on the use of implements would a spec have to follow to dodge this
bullet? SVG2 is still evolving, so I suspect it could adjust its use of
implements if it's an issue for us.
SVG2 does not require any inter process communication. The QueryInterface was
an example of Adam what we should not implement. SVG2 uses WebIDL's
implements statement for [NoInterfaceObject] interfaces, as the HTML
specification is doing it. But SVG uses multiple implements statements per
interface:
interface SVGViewSpec
{
readonly attribute SVGTransformList transform;
readonly attribute SVGElement viewTarget;
readonly attribute DOMString viewBoxString;
readonly attribute DOMString preserveAspectRatioString;
readonly attribute DOMString transformString;
readonly attribute DOMString viewTargetString;
};
SVGViewSpec implements SVGFitToViewBox;
SVGViewSpec implements SVGZoomAndPan;
SVGFitToViewBox and SVGZoomAndPan are both NoInterfaceObjects.
I hope that I am not mistaken and that this is not what you mean with
QueryInterface.
If SVG2 does happen to avoid the problem, would we want to use implements
as the syntax in WebKitIDL or would we want a different syntax? I could see
arguments either way.
I think it would be desirable to follow WebIDL and the syntax of this
specifications as long as the goals overlap.
(FWIW I agree that we don't want to end up in a position where we'd have to
implement a QI-like mechanism for the sake of the bindings, but I can't tell
from the conversation so far if this is an immediate issue with SVG2, or just
a possible issue with other potential uses of implements).
If I understand Adam correctly, then the later. If there are problems with the
SVG2 specification, then I am happy to talk with the SVG WG and find solutions.
But the SVG WG still needs to cover the behavior of SVG 1.1 as much as possible.
Greetings,
Dirk
Regards,
Maciej
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Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 8:09 PM, Dirk Schulze dschu...@adobe.com wrote:
On Jan 25, 2013, at 4:23 PM, Maciej Stachowiak m...@apple.com wrote:
On Jan 25, 2013, at 4:13 PM, Adam Barth aba...@webkit.org wrote:
On Fri, Jan 25, 2013 at 2:08 PM, Dirk Schulze dschu...@adobe.com
wrote:
On Jan 25, 2013, at 9:14 AM, Adam Barth aba...@webkit.org wrote:
On Fri, Jan 25, 2013 at 8:11 AM, Dirk Schulze dschu...@adobe.com
wrote:
This is a followup to the multiple inheritance discussion.
Adam, I checked the IDL files on SVG2 [1]. The interfaces for SVG2
do not have multiple inheritances of interfaces that are exposed to
bindings. But SVG2 still uses the implements statement for
[NoInterfaceObject] interfaces [2]. This should at least address your
initial concern not to inherit from different interfaces exposed to
bindings.
However, during a discussion on IRC I got the impression that we do
not plan to support the implements statement because it can do weird
things. If this is right, I would like to understand why this is the case?
We don't intend to support all the possible things that you can do
with implements. With implements, you can define arbitrarily
complicated relationships between interfaces, including some that can
be implemented only with a QueryInterface-like mechanism. We're not
going to implement QueryInterface, so we're not going to implement any
specifications that require it.
This sounds that you consider having implements in our WebIDL
interpreter, or at least would not block adding this per se. This was my
concern in the first place, since this is already in use in a lot of
specifications (just with [NoInterfaceObject] as far as I saw).
WebKit doesn't have an WebIDL interpretor. We have a WebKitIDL
compiler. If you spec something that requires a QueryInterface-like
mechanism in the implementation, we will not implement it regardless
of what language you write the specification in. It's a conscious
design decision not to implement a COM-like (or XPCOM-like) system.
Setting aside the more general question, does the SVG2 set of interfaces
effectively require a QueryInterface-like mechanism? What limitations, if
any, on the use of implements would a spec have to follow to dodge this
bullet? SVG2 is still evolving, so I suspect it could adjust its use of
implements if it's an issue for us.
SVG2 does not require any inter process communication. The QueryInterface
was an example of Adam what we should not implement. SVG2 uses WebIDL's
implements statement for [NoInterfaceObject] interfaces, as the HTML
specification is doing it. But SVG uses multiple implements statements
per interface:
interface SVGViewSpec
{
readonly attribute SVGTransformList transform;
readonly attribute SVGElement viewTarget;
readonly attribute DOMString viewBoxString;
readonly attribute DOMString preserveAspectRatioString;
readonly attribute DOMString transformString;
readonly attribute DOMString viewTargetString;
};
SVGViewSpec implements SVGFitToViewBox;
SVGViewSpec implements SVGZoomAndPan;
SVGFitToViewBox and SVGZoomAndPan are both NoInterfaceObjects.
I hope that I am not mistaken and that this is not what you mean with
QueryInterface.
Since they're NoInterfaceObjects we can just merge the idl into the file in
WebKit or use Supplemental in WebkitIDL. You've written it with multiple
implements to be DRY in the WebIDL, that's not a problem for WebKit.
See: HTMLInputElementFileSystem.
- E
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Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Jan 25, 2013, at 8:16 PM, Elliott Sprehn espr...@chromium.org wrote:
interface SVGViewSpec
{
readonly attribute SVGTransformList transform;
readonly attribute SVGElement viewTarget;
readonly attribute DOMString viewBoxString;
readonly attribute DOMString preserveAspectRatioString;
readonly attribute DOMString transformString;
readonly attribute DOMString viewTargetString;
};
SVGViewSpec implements SVGFitToViewBox;
SVGViewSpec implements SVGZoomAndPan;
SVGFitToViewBox and SVGZoomAndPan are both NoInterfaceObjects.
I hope that I am not mistaken and that this is not what you mean with
QueryInterface.
Since they're NoInterfaceObjects we can just merge the idl into the file in
WebKit or use Supplemental in WebkitIDL. You've written it with multiple
implements to be DRY in the WebIDL, that's not a problem for WebKit.
See: HTMLInputElementFileSystem.
As far as I understood it, HTMLInputElementFileSystem extends HTMLInputElement.
In WebIDL it would be:
HTMLInputElement implements HTMLInputElementFileSystem;
The problem is that SVGFitToViewBox and SVGZoomAndPan of the example above are
implemented by a lot of other interfaces as well. Supplemental is just supposed
to be set once per interface. That is why Supplemental doesn't work for SVG.
The alternative would be to implement the attributes and operations of
SVGFitToViewBox and SVGZoomAndPan into every class that implements them. This
would be a lot of code copies. And these are not the only interfaces that would
need to be merged.
Greetings,
Dirk
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Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 11:32 PM, Dirk Schulze dschu...@adobe.com wrote: ... The problem is that SVGFitToViewBox and SVGZoomAndPan of the example above are implemented by a lot of other interfaces as well. Supplemental is just supposed to be set once per interface. That is why Supplemental doesn't work for SVG. The alternative would be to implement the attributes and operations of SVGFitToViewBox and SVGZoomAndPan into every class that implements them. This would be a lot of code copies. And these are not the only interfaces that would need to be merged. That's an issue of being DRY though, which we can certainly solve in WebKit. I don't think Adam has an issue with extending webkit IDL to help with that, or at least I'd hope not. We could probably use multiple inheritance in C++ and copy/paste the idl defs, or add some new IDL feature for it. - E ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
Re: [webkit-dev] WebIDL implementation plans (was: Re: Multiple inheritance in the DOM)
On Fri, Jan 25, 2013 at 8:59 PM, Elliott Sprehn espr...@chromium.org wrote: On Fri, Jan 25, 2013 at 11:32 PM, Dirk Schulze dschu...@adobe.com wrote: ... The problem is that SVGFitToViewBox and SVGZoomAndPan of the example above are implemented by a lot of other interfaces as well. Supplemental is just supposed to be set once per interface. That is why Supplemental doesn't work for SVG. The alternative would be to implement the attributes and operations of SVGFitToViewBox and SVGZoomAndPan into every class that implements them. This would be a lot of code copies. And these are not the only interfaces that would need to be merged. That's an issue of being DRY though, which we can certainly solve in WebKit. I don't think Adam has an issue with extending webkit IDL to help with that, or at least I'd hope not. Nope. :) We could probably use multiple inheritance in C++ and copy/paste the idl defs, or add some new IDL feature for it. We already have support for that in WebKitIDL (albeit using a different syntax). See, for example, http://trac.webkit.org/browser/trunk/Source/WebCore/svg/SVGGElement.idl The problem arises if there's an API somewhere that returns, e.g., SVGTransformable. When implementing such an API, we wouldn't know which concrete type we actually have and would need to use something like QueryInterface to find out. Fortunately, no such APIs exist currently. I should also say that we've caved slightly on this stance for interaces like Event that have many subclasses and are often returned by APIs. The way we handle this case is by introducing a virtual function called interfaceName that returns the name of the most-derived interface that the concrete object supports: http://trac.webkit.org/browser/trunk/Source/WebCore/dom/Event.h#L121 At runtime, we use that information to static_cast the C++ object appropriately. It's not as general as QueryInterface, and I'm not sure how far we want to extend that mechanism given that it's relatively slow. Certainly we wouldn't want to introduce a universal base class (a la IUnknown or nsISupports) as required in COM and XPCOM, respectively. Adam ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
