silk.core.ownership.

When to use#

Use Copy to declare that a type duplicates on assignment, or as a bound on a type parameter that generic code duplicates. Use Drop to give an affine type a cleanup operation that runs when a value goes out of scope.

Details#

Both names are transparent type aliases (TYPE-004) of the compiler-sealed properties Intrinsic.Copy and Intrinsic.Drop (INTR-006). impl Copy for Point {} and impl Intrinsic.Copy for Point {} are the same conformance. An import of these names gives no special permission. The rules of each property (OWN-001, STRUCT-005) decide which types can conform.

Gotchas#

The names are ordinary names. A local declaration named Copy, or a type parameter named Drop, hides the import.

Examples#

Duplicate a value through a bound#

import silk.core.ownership { Copy }

struct Point {
  x: i32,
  y: i32,
}

impl Copy for Point {}

fn pair<T: Copy>(value: T) -> [T; 2] {
  // `value` is used two times. The `Copy` bound makes this legal.
  return [value, value]
}

pub fn main() -> i32 {
  let points = pair(Point { x: 1, y: 2 })
  if points[1].y != 2 {
    return 1
  }
  return 0
}

Import as Copy with import silk.core.ownership { Copy }.

Public declarations: 2.

Copy#

pub type Copy = Intrinsic.Copy

The property of types whose values duplicate on assignment, with no user code.

Details#

Declare it with an empty conformance, as in impl Copy for Point {}. A type can conform only if each of its fields is Copy and the type has no Drop conformance. Use T: Copy as a bound when generic code uses a value of type T more than one time.

Drop#

pub type Drop = Intrinsic.Drop

The property of affine types that run one cleanup operation when a value is dropped.

Details#

A conformance gives the member drop(self: &mut Self) -> (). The member runs one time for each value, when the value goes out of scope or at an explicit drop. The member does not run for a value that was moved away. After the member returns, the fields of the value are dropped.

Gotchas#

A type with a Drop conformance cannot be Copy.

Category: Core.

Profiles: aarch64-apple-darwin, aarch64-unknown-linux-gnu, aarch64-unknown-linux-gnu-no-libc, x86_64-unknown-linux-gnu, x86_64-unknown-linux-gnu-no-libc, wasm32-unknown-unknown, wasm32-wasip1, wasm32-wasip2.