[swift-evolution] [Pitch] Swift needs fixed-size array

[Michael Ilseman]

My understanding is that there is no mechanism yet to guarantee stack allocation for anything.

> On Apr 17, 2017, at 3:29 PM, Karl Wagner <razielim at gmail.com> wrote:
> 
> 
>> On 17 Apr 2017, at 23:18, Michael Ilseman via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> This is the best approach that I’m aware of. It does bake in an ABI assumption that the tuple layout will be contiguous and strided/addressable. Monitor https://bugs.swift.org/browse/SR-3726 <https://bugs.swift.org/browse/SR-3726> for changes here. Note that you can also a little more “pure” in a sense if you construct an UnsafeBufferPointer from your UnsafeRawPointer and operate on that. Currently, the compiler does not always elide the copy in the getter, see https://bugs.swift.org/browse/SR-4581 <https://bugs.swift.org/browse/SR-4581>
>> 
> 
> Will the compiler ever optimise an UBP allocation on to the stack? For example, I’ve written plenty of code such as:
> 
> let ptr = UnsafeRawBufferPointer.allocate(count: 128)
> defer { ptr.deallocate(count: 128) }
> 
> ...when interfacing with C APIs. Which is basically the definition of a stack allocation. That would perhaps be the “swiftier” way to do it; to let the compiler determine how to allocate the memory based on what it knows about its expected lifetime.

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