> On Dec 21, 2015, at 1:49 PM, Chris Lattner via swift-evolution
> <[email protected]> wrote:
>
>
>> On Dec 21, 2015, at 12:05 PM, Jacob Bandes-Storch <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> On Mon, Dec 21, 2015 at 11:55 AM, Chris Lattner via swift-evolution
>> <[email protected] <mailto:[email protected]>> wrote:
>> …there probably has to be some way to unsafely “force a call to a non-pure
>> function to be allowed in a pure one”, both because of type system
>> limitations as well as interoperability with C and other languages. Even
>> ignoring issues around errno, it would be sad for a pure function to not be
>> able to call “sin(x)” just because it weren’t marked __attribute__((const)).
>>
>> Minor tangent, but should the same apply to @noescape?
>
> Yes, it should. I believe you can currently use an unsafe cast to remove
> @noescape, and that the stdlib does it in a few places. Dmitri, do you know
> where?
The runtime does this using unsafeBitCast, but don't follow its example—I don't
want to promise this will always be possible. There are representation
optimizations we can do with @noescape closures that would be blocked if they
always had to be bitcastable to refcounted escapable closures. I'd like to
introduce a `Builtin.makeEscapable` operation specifically to go from @noescape
to escapable, introducing a refcounting shim if necessary in the future.
-Joe
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