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

Taylor Swift kelvin13ma at gmail.com
Wed Jul 19 22:33:37 CDT 2017

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,

:[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

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.
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