[swift-evolution] [Review] SE-0136: Memory Layout of Values

[Brandon Knope]

I feel so incredibly silly :facepalm:

Thank you...it's obvious now

Brandon 

Sent from my iPad

> On Aug 7, 2016, at 11:21 PM, Dave Abrahams <dabrahams at apple.com> wrote:
> 
> 
>> on Sun Aug 07 2016, Brandon Knope <bknope-AT-me.com> wrote:
>> 
>> Yes but:
>> 
>> extension MemoryLayout {
>>  @_transparent
>>  public static func size(ofValue _: T) -> Int {
>>    return MemoryLayout.size
>>  }
>>  @_transparent
>>  public static func stride(ofValue _: T) -> Int {
>>    return MemoryLayout.stride
>>  }
>>  @_transparent
>>  public static func alignment(ofValue _: T) -> Int {
>>    return MemoryLayout.alignment
>> Vs
>> 
>> public struct MemoryLayout<T> { 
>>     public static var size: Int { return _sizeof(T) } 
>>     public static var stride: Int { return _strideof(T) } 
>>     public static var alignment: Int { return _alignof(T) }
>> }
>> 
>> I see the obvious difference between the two in their names and signature, but what is the need for both?
>> 
>> It looks duplicated for the most part, so some clarification would be nice. 
> 
> The use case is this: you have a value, but you don't have its type at
> compile-time, and you want memory layout information.  For example, it
> might be the result of
> 
>     let x = (0..<20).reversed().lazy.map { $0 * 3 }
> 
> (which has a horrible type you wouldn't want to spell out) and you want
> to know the size of the instance x.
> 
>     MemoryLayout.size(ofValue: x)
> 
> will work here.  Getting a type to pass in the angle brackets requires
> jumping through lots of hoops and is easy to get wrong.
> 
> -- 
> -Dave