downcast<> fails if you do a useless cast/upcast.
Benjamin
On 10/2/14, 4:47 PM, Sam Weinig wrote:
This all looks wonderful!
One question though, why downcast<>(…)? Will we be adding an upcast<>()
function? Since the answer is probably no, could we just call this
cast<>(…)?
- Sam
On Sep 25, 2014, at 11:11 AM, Chris Dumez <[email protected]
<mailto:[email protected]>> wrote:
Hi all,
I started working on automatically generating the type *casting*
helpers for HTML/SVG/MathML Elements (e.g. toHTMLDivElement()). Until
now, we were generating only the type *checking* helpers using
make_names.pl (e.g. isHTMLDivElement()). The type *casting* helpers
had to be manually defined using NODE_TYPE_CASTS() macro.
The type casting helpers are now automatically generated for most
types. Part of the solution involved using a templated function for
type casting because the types are forward-declared and we needed to
do a static_cast<>() (a reinterpret_cast<>() could be used with
forward declarations but wouldn’t be safe due to multiple inheritance).
I initially had macros in place so that toHTMLDivElement() would still
work and would be equivalent to downcast<HTMLDivElement>(). The
feedback I received is that we should get rid of these macros and just
use is<HTMLDivElement>() / downcast<HTMLDivElement>() everywhere.
The new style is very close to C++’s is_class<T>() and Boost’s
polymorphic_downcast<T>().
I actually started updating the code to do this but I should have
emailed webkit-dev about this beforehand. I apologize for sending this
message a bit late.
Please let me know if you have feedback / concerns / questions about
this change. I hope that this email gives you a better understanding
of why I am making this change.
As I said before, the code base is not fully ported yet so the current
situation is not necessarily pretty. I will try and go through the
transition as fast as I can, provided that people don’t raise any
concerns about this.
Please also note that these new helpers still catch unnecessary type
checks / casts. As a matter of fact, those are now caught at build
time instead of linking time and should give you a nice “Unnecessary
type check” / “Unnecessary type cast” static assertion.
Also note that the plan is to get rid of TYPE_CAST_BASE() macro
entirely and extend is<>() / downcast<>() to all types, not just Nodes.
Kr,
--
Chris Dumez - Apple Inc.
Cupertino, CA
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