> On Aug 3, 2016, at 2:43 PM, Dave Abrahams via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>
> Having seen the effects in the standard library and in other
> code, I'm concerned that we may have made a mistake in removing
> `sizeofValue` et al without providing a replacement. In the standard
> library, we ended up adding an underscored API that allows
>
> MemoryLayout._ofInstance(someExpression).size
>
> Where someExpression is an autoclosure, and thus not evaluated. I
> wanted to bring up the possibility of introducing a replacement as a
> bufix.
>
> I propose that the way to express the above should be:
>
> MemoryLayout.of(type(of: someExpression)).size
>
> implementable as:
>
> extension MemoryLayout {
> @_transparent
> public
> static func of(_: T.Type) -> MemoryLayout<T>.Type {
> return MemoryLayout<T>.self
> }
> }
>
> I think this API would solve the concerns I had about confusability that
> led me to advocate dropping the ability to ask for the size of a value.
> The only way to use it is to pass a type and these two expressions have
> equivalent meaning:
>
> MemoryLayout<Int>
> MemoryLayout.of(Int.self)
>
> It also has the benefit of isolating the autoclosure magic to type(of:).
>
> ,----[ Aside ]
> | A slightly cleaner use site is possible with a larger API change:
> |
> | MemoryLayout(type(of: someExpression)).size
> |
> | Which would involve changing MemoryLayout from an `enum` to
> | a `struct` and adding the following:
> |
> | extension MemoryLayout {
> | public init(_: T.Type) {}
> |
> | public var size: Int { return MemoryLayout.size }
> | public var stride: Int { return MemoryLayout.stride }
> | public var alignment: Int { return MemoryLayout.alignment }
> | }
> |
> | However I am concerned that dropping ".of" at the use site is worth the
> | added API complexity.
> `----
>
> Thoughts?
> --
> -Dave
I don't think using "of" is a great burden.
-- E
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