> On Nov 2, 2016, at 10:37 AM, Rien via swift-users <swift-users@swift.org>
> wrote:
>
>>> var rawPtr = UnsafeMutableRawPointer.allocate(bytes: 2, alignedTo: 0)
>>>
>>> var widePtr = rawPtr.bindMemory(to: Int16.self, capacity: 1)
>>>
>>> widePtr.pointee = 32
>>>
>>> var narrowPtr = rawPtr.bindMemory(to: UInt8.self, capacity: 2)
>>>
>>> narrowPtr[0] = 16
>>> narrowPtr[1] = 255
>>>
>>> print(widePtr.pointee)
>>
>> This compiles and runs as expected, but it should not be allowed if I
>> understand things correctly. So shouldn’t it be a compile time error or
>> crash at runtime? If not, what do I get over how it was before where I was
>> casting to a typed pointer?
>
> Why do you think it should not be allowed.
> AFAICS everything is correct.
> Are you referring to the multiple interpretation of the raw memory? That is
> entirely intentional, indeed one of the main purposes.
Allowing type punning is one of the main purposes of raw memory access (via a
raw pointer). But in this code, widePtr.pointee is a typed UInt16 load from
memory that is bound to UInt8. Loading a UInt16 without rebinding memory first
requires a raw load such as:
rawPtr.load(as: UInt16.self)
-Andy
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