[Feature Request] Merge init_pointee_move and move_pointee_into.

[soraros]

Review Mojo's priorities

• I have read the roadmap and priorities and I believe this request falls within the priorities.

What is your request?

As title.

What is your motivation for this change?

If I understand correctly, we don't need both.

Any other details?

N/A

[bethebunny]

init_pointee_move treats the input as "uninit", which means it won't call the destructor on whatever data is in the pointer already, whereas move_pointee_into will call the destructor of the old data before the move.

[soraros]

@bethebunny So s.move_pointee_into(t) is t.init_pointee_move(s.take_pointee())?

[bethebunny]

s.move_pointee_into(t) should be equivalent to

_ = t.take_pointee()
t.init_pointee_move(s.take_pointee())

[soraros]

But the doctoring of move_pointee_into says that dst is assumed to be uninitialised, so it doesn't run the destructor.

If it calls the destructor of the old data, why can't we write

t[] = s[]^

[soraros]

The really difference seems to be that t.init_pointee_move(s.take_pointee()) calls moveinit twice.

struct S:
  var data: Float64

  fn __init__(inout self, data: Float64):
    self.data = data

  fn __copyinit__(inout self, other: S):
    print("  copyinit", other.data)
    self.data = other.data

  fn __moveinit__(inout self, owned other: S):
    print("  moveinit", other.data)
    self.data = other.data

  fn __del__(owned self):
    print("  del", self.data)

fn move_pointee_into():
  print("move_pointee_into:")
  var v = S(10)
  var t = UnsafePointer[S].alloc(1)
  var s = UnsafePointer.address_of(v)
  s.move_pointee_into(t)
  print()
  _ = v

fn init_pointee_move():
  print("init_pointee_move:")
  var v = S(20)
  var t = UnsafePointer[S].alloc(1)
  var s = UnsafePointer.address_of(v)
  t.init_pointee_move(s.take_pointee())
  print()
  _ = v

fn main():
  move_pointee_into()
  print()
  init_pointee_move()

Result:

move_pointee_into:
  moveinit 10.0

  del 10.0

init_pointee_move:
  moveinit 20.0
  moveinit 20.0

  del 20.0