> On Apr 22, 2016, at 8:48 PM, Charles Srstka via swift-evolution
> <[email protected]> wrote:
>
>>> On Apr 22, 2016, at 5:05 PM, Greg Parker <[email protected]> wrote:
>>>
>>> On Apr 22, 2016, at 2:36 PM, Charles Srstka via swift-evolution
>>> <[email protected]> wrote:
>>>
>>> One comment:
>>>
>>> "In the most common case where a developer does not provide a custom
>>> reference type, then the backing store is our existing NSData and
>>> NSMutableData implementations. This consolidates logic into one place and
>>> provides cheap bridging in many cases (see Bridging for more information).”
>>>
>>> Would it not be more efficient to bridge to the C-based CFData and
>>> CFMutableData implementations instead, to avoid the object overhead?
>>
>> Not necessarily. Foundation often has less overhead than CF nowadays.
>
> That’s interesting; I hadn’t known that. What causes that? My understanding
> had always been that the NS and CF objects, being toll-free bridged to each
> other, shared the same default implementations, with the only difference
> being that the NS versions involved the overhead from objc_msgSend() as well
> as, in many cases, an autorelease.
>
> Charles
There's a wide variety of bridging techniques in use, but in NSData's case the
implementations are separate (and there are 5 implementations for NSData, 1 for
CFData). CFData also has to pay the cost for detecting whether it's argument is
a bridged NSData, which is ironically about as expensive as a message send.
David
>
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