[swift-evolution] [swift-evolution-announce] [Review #2] SE-0101: Reconfiguring sizeof and related functions into a unified MemoryLayout struct

[Xiaodi Wu]

On Mon, Jul 18, 2016 at 10:57 AM, Erica Sadun via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On Jul 13, 2016, at 5:39 PM, Dave Abrahams via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> on Wed Jul 13 2016, Brent Royal-Gordon <swift-evolution at swift.org> wrote:
>
> I think grouping these into a type is a sensible approach, but I don't
> like that
> * it allows the creation of meaningless MemoryLayoutinstances*. The
> simplest fix would be to make `MemoryLayout` an empty
> enum instead of an empty struct. This would convey that no
> MemoryLayout instances do or can exist.
>
>
> +1.
>
>
> +1 as well.
>

I must be missing something. How would one create MemoryLayout instances
without a public initializer? Why would it matter if stdlib could formally
do so internally, given the plethora of much less harmless things that
stdlib can do internally?

/// Accesses the memory layout of `T` through its
>
> /// `size`, `stride`, and `alignment` properties
> public enum MemoryLayout {
>     /// Returns the contiguous memory footprint of `T`.
>     ///
>     /// Does not include any dynamically-allocated or "remote"
>     /// storage. In particular, `MemoryLayout.size`, when
>     /// `T` is a class type, is the same regardless of how many
>     /// stored properties `T` has.
>     public static var size: Int { return _sizeof(T.self) }
>
>     /// For instances of `T` in an `Array`, returns the number of
>     /// bytes from the start of one instance to the start of the
>     /// next. This is the same as the number of bytes moved when an
>     /// `UnsafePointer` is incremented. `T` may have a lower minimal
>     /// alignment that trades runtime performance for space
>     /// efficiency. The result is always positive.
>     public static var stride: Int { return _strideof(T.self) }
>
>     /// Returns the default memory alignment of `T`.
>     public static var alignment: Int { return _alignof(T.self) }
> }
>
>
>
> -- E
>
>
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