Module slot

Explicit stack slots, which can be used for stack emplacement.

A Slot is uninitialized storage on the stack that can be manipulated explicitly. Notionally, a Slot<T> represents a let x: T; in some function’s stack.

Slots mut be created with the slot!() macro:

slot!(storage);
let mut x = storage.put(42);
*x /= 2;
assert_eq!(*x, 21);

Unfortunately, due to the constrains of Rust today, it is not possible to produce a Slot as part of a larger expression; since it needs to expand to a let to bind the stack location, slot!() must be a statement, not an expression.

Slots can also be used to implement a sort of “guaranteed RVO”:

fn returns_on_the_stack(val: i32, storage: Slot<i32>) -> Option<MoveRef<i32>> {
  if val == 0 {
    return None
  }
  Some(storage.put(val))
}

slot!(storage);
let val = returns_on_the_stack(42, storage);
assert_eq!(*val.unwrap(), 42);

Slots provide a natural location for emplacing values on the stack. The moveit!() macro is intended to make this operation straight-forward.

DroppingSlot

DroppingSlot is a support type similar to Slot that is used for implementing DerefMove, but which users should otherwise not construct themselves (despite it being otherwise perfectly safe to do so).

Structs

DroppingSlot

Similar to a Slot, but able to drop its contents.

Slot

An empty slot on the stack into which a value could be emplaced.