[swift-users] Can I use a tuple to force a certain memory layout?

[David Sweeris]

> On Jul 19, 2017, at 20:33, Taylor Swift via swift-users <swift-users at swift.org> wrote:
> 
> Many APIs like OpenGL take arrays where the atomic unit is multiple elements long. For example, a buffer of coordinates laid out like 
> 
> :[Float] = [ x1, y1, z1, x2, y2, z2, ... , xn, yn, zn ]
> 
> I want to be able to define in Swift (i.e., without creating and importing a Objective C module) a struct that preserves the layout, so that I can do withMemoryRebound(to:capacity:_) or something similar and treat the buffer as 
> 
> struct Point 
> {
>     let x:Float, 
>         y:Float, 
>         z:Float
> }
> 
> :[Point] = [ point1, point2, ... , pointn ]
> 
> The memory layout of the struct isn’t guaranteed, but will the layout be guaranteed to be in declaration order if I use a tuple inside the struct instead?
> 
> struct Point 
> {
>     let _point:(x:Float, y:Float, z:Float)
> 
>     var x:Float 
>     {
>         return self._point.x
>     }
> 
>     var y:Float 
>     {
>         return self._point.y
>     }
> 
>     var z:Float 
>     {
>         return self._point.z
>     }
> }
> 
> This is an ugly workaround, but I can’t really think of any alternatives that don’t involve “import something from Objective C”. I am aware that the implementation of structs currently lays them out in declaration order, but I’m looking for something that’s actually defined in the language.

IIRC, Swift doesn't have a way to get a guaranteed memory layout yet, other than defining the type in C (or Obj-C) and importing it.

- Dave Sweeris
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