[swift-evolution] [Pitch] deprecating ManagedBufferPointer

[Erik Eckstein]

I created a proposal: https://github.com/apple/swift-evolution/pull/545 <https://github.com/apple/swift-evolution/pull/545>

> On Oct 11, 2016, at 11:32 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> on Tue Oct 11 2016, Károly Lőrentey <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> +1
>> 
>> ManagedBuffer has been really useful a couple of times, but I never
>> found a use for ManagedBufferPointer. I can’t even say I’m entirely
>> sure what need it was originally designed to fulfill.
> 
> The real need is/was to be able to do the same kind of storage
> management in classes not derived from ManagedBuffer.  This can be
> important for bridging, where the buffers of various native swift
> containers need to be derived from, e.g., NSString or NSArray.  That is,
> however, an extremely stdlib-specifc need.
> 
> 
>>> On 2016-10-11, at 00:12, Erik Eckstein via swift-evolution
>> <swift-evolution at swift.org> wrote:
>>> 
>>> The purpose of ManagedBufferPointer is to create a buffer with a custom class-metadata to be able
>> to implement a custom deinit (e.g. to destroy the tail allocated elements).
>>> It was used in Array (before I replaced it with the new tail-allocated-array-built-ins). But now
>> it’s not used anymore in the standard library.
>>> 
>>> As a replacement for ManagedBufferPointer one can just derive a class from ManagedBuffer and implement the deinit in the derived class.
>>> 
>>> final class MyBuffer : ManagedBuffer<MyHeader, MyElements> {
>>>  deinit {
>>>    // do whatever needs to be done
>>>  }
>>> }
>>> 
>>> // creating MyBuffer:
>>> let b = MyBuffer.create(minimumCapacity: 27, makingHeaderWith: { myb in return MyHeader(...) })
>>> 
>>> IMO ManagedBuffer is much cleaner than ManagedBufferPointer (it doesn’t need this custom
>> bufferClass to be passed to the constructor). Also ManagedBufferPointer doesn’t use SIL
>> tail-allocated arrays internally. Although this is not something visible to the programmer, it makes
>> life easier for the compiler.
>>> 
>>> So I suggest that we deprecate ManagedBufferPointer.
>>> 
>>> Erik
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>> 
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> 
> -- 
> -Dave
> 
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