[swift-users] Exclamation mark's in swift parameter listings?

[Slava Pestov]

For what it’s worth, if T is a reference type or Unsafe*Pointer, then T and Optional<T> have the same exact representation in memory.

The compiler is smart enough to know that a non-optional pointer can never be NULL, so a NULL value of the underlying type can be used to unambiguously encode the ‘none’ case. This is not the case with Optional<NSRect> for example, where every bit pattern represents a potentially valid NSRect value, so Optional<NSRect> has to add an extra tag byte to distinguish the two enum cases from each other.

Slava

> On Jan 10, 2017, at 9:52 AM, Rien via swift-users <swift-users at swift.org> wrote:
> 
> I stand corrected.
> 
> I do/did think that there is a difference in the way it handles pointers optionals and other optionals, but I now realise that even that could not be the case.
> So please ignore the last line in my previous post.
> 
> The rest still stand ;-)
> 
> Regards,
> Rien
> 
> Site: http://balancingrock.nl
> Blog: http://swiftrien.blogspot.com
> Github: http://github.com/Swiftrien
> Project: http://swiftfire.nl
> 
> 
> 
> 
>> On 10 Jan 2017, at 18:14, Joe Groff <jgroff at apple.com> wrote:
>> 
>> 
>>> On Jan 9, 2017, at 11:19 PM, Rien via swift-users <swift-users at swift.org> wrote:
>>> 
>>> It means that a call to that function with an optional will unwrap the optional before it is used.
>>> 
>>> That is quite neat when dealing with C-API’s because often you will receive a pointer from a C-function which is optional to account for the fact that it can be NULL (= nil).
>>> By using a forced unwrapped input parameter you are saved the trouble of unwrapping all these pointers when using them as input for other C-APIs.
>>> 
>>> In short, it makes it easier to interface with C-API’s.
>>> 
>>> Note that there is some under-the-hood magic going on because a C-pointer is an unboxed value, while a ‘normal’ optional is a boxed value.
>> 
>> Optionals are never boxed.
>> 
>> -Joe
> 
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