as-and-ref.md

minutes	5

as_ and _ref: reference conversions

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
impl<T> Rc<T> {
    // Very common on container types, see how it's also on Option.
    fn as_ref(&self) -> &T;

    fn as_ptr(&self) -> *const T;
}

impl<T> Option<T> {
    fn as_ref(&self) -> Option<&T>;

    fn as_slice(&self) -> &[T];
}

Details

• Method that returns a borrow of the primary piece of contained data.

• The borrowing relationship is most often straightforward: the return value is a reference that borrows self.

• The returned value could borrow self only logically, for example, as_ptr() methods return an unsafe pointer. The borrow checker does not track borrowing for pointers.

• The type implementing an "as" method should contain one primary piece of data that is being borrowed out.

  • The "as" naming convention does not work if the data type is an aggregate of many fields without an obvious primary one.

  • If you have two reference getters that you need to distinguish, use the _ref suffix.