[swift-evolution] [Pitch] deprecating ManagedBufferPointer

[Dave Abrahams]

on Tue Oct 11 2016, Károly Lőrentey <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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-- 
-Dave