> On Oct 4, 2016, at 3:06 PM, David Vandevoorde <[email protected]> wrote:
>> On Oct 4, 2016, at 5:54 PM, John McCall <[email protected]
>> <mailto:[email protected]>> wrote:
> […]
>> What we did for ARM64 seems like the right basic approach: the type_info
>> object records whether it's unique or non-unique, and non-unique RTTI just
>> falls back on string-based comparisons / hashes. The type_info is unique if
>> and only if it's for a fundamental type in the ABI library or a polymorphic
>> class with a key function.
>
> That sounds pretty good, but can it be done in a backward-compatible way?
> I’m guessing not, but perhaps it’s “close enough”?
If you still made every effort to coalesce type_info names even for non-unique
RTTI, and you found a way to record non-uniqueness that didn't mess up existing
compiles, then interoperation would generally remain intact. However, in my
mind that would sacrifice the main benefit, which is that non-unique RTTI no
longer require default visibility. I should have been clear that I was noting
this mostly as an "ABI v2" recommendation.
John.
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