[swift-evolution] [RFC] UnsafeBytePointer API for In-Memory Layout

[Andrew Trick]

> On May 9, 2016, at 1:20 PM, Joe Groff <jgroff at apple.com> wrote:
> 
> Regarding the UnsafeBytePointer API:
> 
>> struct UnsafeBytePointer : Hashable, _Pointer {
>> 
>>   let _rawValue: Builtin.RawPointer
>> 
>>   var hashValue: Int {...}
>> 
>>   init<T>(_ : UnsafePointer<T>)
>>   init<T>(_ : UnsafeMutablePointer<T>)
>>   init?<T>(_ : UnsafePointer<T>?)
>>   init?<T>(_ : UnsafeMutablePointer<T>?)
>> 
>>   init<T>(_ : OpaquePointer<T>)
>>   init?<T>(_ : OpaquePointer<T>?)
>> 
>>   init?(bitPattern: Int)
>>   init?(bitPattern: UInt)
>> 
>>   func load<T>(_ : T.Type) -> T
>> 
>>   @warn_unused_result
>>   init(allocatingBytes size: Int, alignedTo: Int)
>> 
>>   @warn_unused_result
>>   init<T>(allocatingCapacity count: Int, of: T.Type)
>> 
>>   func deallocateBytes(_ size: Int, alignedTo: Int)
>> 
>>   func deallocateCapacity<T>(_ num: Int, of: T.Type)
>> 
>>   // Returns a pointer one byte after the initialized memory.
>>   func initialize<T>(with newValue: T, count: Int = 1) -> UnsafeBytePointer
>> 
>>   // Returns a pointer one byte after the initialized memory.
>>   func initialize<T>(from: UnsafePointer<T>, count: Int) -> UnsafeBytePointer
>> 
>>   func initializeBackward<T>(from source: UnsafePointer<T>, count: Int)
>> 
>>   func deinitialize<T>(_ : T.Type, count: Int = 1)
>> }
> 
> Should we also have 'assign' methods, matching 'initialize'? Should 'deinitialize' be called 'destroy', matching 'UnsafeMutablePointer's API?

I was wondering if anyone would ask for ‘assign’. It presumes that you are storing the same type of object that was previously stored in your buffer. I didn’t want to proactively support that case because it’s a convenience and not really consistent with the pointer being type punned. You can always call deinitialize() first if you need to before calling ‘initialize'. I  used ‘deinitialize’ to be consistent with UnsafeMutablePointer.

-Andy

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