> On Jun 30, 2016, at 12:30, Dave Abrahams via swift-evolution
> <swift-evolution@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@swift.org> wrote:
>>>
>>> On Wed, Jun 29, 2016 at 4:50 PM, David Sweeris <daveswee...@mac.com
>>> <mailto:daveswee...@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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