[swift-dev] inefficient enum layout with optionals

[Kelvin Ma]

i noticed that this enum takes up 9 bytes of storage

  1> enum QuantizationTable
  2. {
  3.     case q8 (UnsafeMutablePointer<UInt8>),
  4.          q16(UnsafeMutablePointer<UInt16>)
  5. }
  6> MemoryLayout<QuantizationTable>.size
$R0: Int = 9

but when i make it optional, it takes up 10

  7> MemoryLayout<QuantizationTable?>.size
$R1: Int = 10

can’t the compiler just tack the nil case onto the original enum as a third
case? after all, this works fine

  1> enum QuantizationTable
  2. {
  3.     case q8 (UnsafeMutablePointer<UInt8>),
  4.          q16(UnsafeMutablePointer<UInt16>),
  5.          none
  6. }
  7> MemoryLayout<QuantizationTable>.size
$R0: Int = 9

the way i’m using it atm it all gets padded to 16 anyway so i don’t care
that much but is this something that’s being looked at?
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