[swift-evolution] [Draft] Target-specific CChar

[Joe Groff]

> On Mar 2, 2016, at 11:06 AM, Dmitri Gribenko via swift-evolution <swift-evolution at swift.org> wrote:
> 
> On Wed, Mar 2, 2016 at 11:03 AM, William Dillon <william at housedillon.com> wrote:
>> It does violate the principle of least astonishment, but we should
>> acknowledge that the implementation-specific nature of C's char signedness
>> is making code *less* portable, not more -- because the same code can mean
>> different things on different platforms.  Reflecting the same in Swift makes
>> Swift code less portable, too.
>> 
>> Dmitri
>> 
>> That is a fair point, and I agree for the most part.  However, It is my
>> intent and expectation that the use of CChar would be limited to the margins
>> where C APIs are imported.  Once values become a part of Swift (and used in
>> places outside of the C interface) they should have been cast into a pure
>> Swift type (such as UInt8, Int8, Int, etc).
> 
> True, but how can you cast a CChar portably into UInt8 or Int8?  Only
> via the bitPattern initializer, because the regular initializer will
> trap on values outside of the 0..<128 range on signed platforms or
> unsigned platforms.

Could we treat CChar as a "signless" byte type, so that UInt8(cchar) and Int8(cchar) both just reinterpret the bit pattern?

-Joe