Witch of Git - ivy/blob - docs/object-layout.md

   1 # Object Layouts
   2
   3
   4 All heap objects have a 32-bit reference count at [obj + 4].
   5 Objects are returned at +1.
   6
   7
   8 Integers:
   9 A 63-bit signed integer, shifted left 1, with the lsb set.
  10 For example, 1 is stored as 0b11, 2 as 0b101, etc.
  11 Can also be stored as an aligned pointer to an object.
  12
  13 TODO: support big ints with this layout.
  14
  15 [u8:tag=1]
  16 [u24:pad]
  17 [u32:refcount]
  18 [i64:value]
  19
  20
  21 Closures:
  22 A pointer to the closure entry.
  23 Must be 8-byte aligned.
  24
  25 00:[u8:tag=0]
  26 01:[u8:pad]
  27 02:[u16:upvars]
  28 04:[u32:refcount]
  29 08:[u64:fn ptr]
  30 10:[u16:params]
  31 12:[u16:filled params]
  32 14:[u32:pad]
  33 18:[params...]
  34 ??:[fields...]
  35
  36
  37 Indirect Closures:
  38 When a closure has lots of data and is frequently copied, it's beneficial to use an indirect closure that contains a pointer to the fields block so that only the params has to be copied.
  39 These are unimplemented for the time being.
  40
  41 00:[u8:tag=2]
  42 01:[u8:pad]
  43 02:[u16:upvars]
  44 04:[u32:refcount]
  45 08:[u64:fn ptr]
  46 10:[u16:params]
  47 12:[u16:filled params]
  48 14:[u32:pad]
  49 18:[params...]
  50 ??:[u64:fields ptr]
  51
  52
  53 fields block:
  54 00:[u16:pad]
  55 02:[u16:field count]
  56 04:[u32:refcount]
  57 08:[fields...]
  58
  59
  60 When a closure is destroyed, it iterates over all of its fields and performs a decref on them.