[swift-evolution] [Review] SE-0101: Rename sizeof and related functions to comply with API Guidelines

[Jordan Rose]

> On Jun 30, 2016, at 12:30, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> on Wed Jun 29 2016, Erica Sadun <erica-AT-ericasadun.com> wrote:
> 
>>> On Jun 29, 2016, at 3:59 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> On Wed, Jun 29, 2016 at 4:50 PM, David Sweeris <davesweeris at mac.com <mailto:davesweeris at mac.com>> wrote:
>>> That’s the “as proposed” usage for getting the size of a value (from
>>> https://gist.github.com/erica/57a64163870486468180b8bab8a6294e
>> 
>>> <https://gist.github.com/erica/57a64163870486468180b8bab8a6294e>)
>>> // Types
>>> MemoryLayout<Int>.size // 8 
>>> MemoryLayout<Int>.arraySpacing // 8
>>> MemoryLayout<Int>.alignment // 8
>>> 
>>> // Value
>>> let x: UInt8 = 5
>>> MemoryLayout(x).dynamicType.size // 1
>>> MemoryLayout("hello").dynamicType.arraySpacing // 24
>>> MemoryLayout(29.2).dynamicType.alignment // 8
>>> 
>>> 
>>> At least, I thought that was the latest version of the proposal. Maybe I’ve gotten confused.
>>> 
>>> There must be a typo in these examples. `MemoryLayout(x.dynamicType).size` perhaps?
>> 
>> I have listened. I have updated.
>> 
>> https://gist.github.com/erica/57a64163870486468180b8bab8a6294e
>> 
>> // Types
>> MemoryLayout<Int>.size // 8
>> MemoryLayout<Int>.arraySpacing // 8
>> MemoryLayout<Int>.alignment // 8
>> 
>> // Value
>> let x: UInt8 = 5
>> MemoryLayout.of(x).size // 1
>> MemoryLayout.of(1).size // 8
>> MemoryLayout.of("hello").arraySpacing // 24
>> MemoryLayout.of(29.2).alignment // 8
> 
> I am still very skeptical that anyone needs the “Value” version, and as
> long as we're resyntaxing I am inclined to take it away and see how many
> people complain.  You can still always write it yourself.

Sorry to only come across this now. The proposed implementation does not work.

public static func of(_ candidate : @autoclosure () -> T) -> MemoryLayout<T>.Type {
  return MemoryLayout.init(candidate).dynamicType
}

let value: Any = 2 // dynamicType is Int
let layout = MemoryLayout(value).dynamicType // inlined from above
let arrayType = [value].dynamicType

‘layout’ here is still 'MemoryLayout<Any>', not 'MemoryLayout<Int>', for the same reason that ‘arrayType’ is ‘Array<Any>’ rather than ‘Array<Int>’.

If we want to support sizeofValue et al, we’d need to make these instance properties rather than static properties, and may then want to give up on the struct being generic.

Jordan

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